An Index to my Flipping Blog Postings

I've had multiple requests for a more convenient format in which to read about my experience flipping CS161, my undergraduate operating systems class, that I've put together this index page. Enjoy.
One Woman's Adventure with a Flipped Classroom (February 4, 2013)
Flipped Again (February 7, 2013)
Not Flipping Out (February 16, 2013)
Addicted to flipping (February 21, 2013)
Unflipped! (March 4, 2013)
Half Flip (March 9, 2013)
Flipping and Testing (March 18, 2013)
Inadvertent Flip (April 1, 2013)
Missing Flipping (April 8, 2013)
Anxiously Flipped (April 15, 2013)
Flipped Out (April 22, 2013)
Flip N-1 (April 30, 2013)
Flipping Over (May 24, 2013)

Flipping Over

We are done. The course is over, except for the data analysis, which I expect to entertain me over the summer. This last entry will be a collection of random topics - things that happened over the course of the final exam and grading or observations I've made.

End of year party

Long ago, in 1993, we started the tradition of having an ice cream bash after the take home final. I don't believe we've maintained the tradition, but I decided to resurrect it. In addition, we continued the tradition of class T-shirts. The winning design was:

In addition, since I had artwork for each group, I made that available to students to construct their own team patch, which they could then iron onto their shirts. Groups who didn't have the time to do anything fancy (21 of 22 groups), got the plain hand-drawn black and white animal.

So, on Wednesday afternoon after spending a lot of time on the final, we all gathered in a much too small room to eat Toscanini's ice cream, collect T-shirts, and iron on patches. It was a total blast. Pretty much everyone ironed their patches. The one group who augmented their animal was the marmots, who added color and appropriate attire:

We had a few ironing disasters which prompted a return to QRSTs for a few additional shirts.

Had I been thinking, I would have tried to get a group shot, but I didn't. Next time! One of my students, did take this small group picture:

Students seemed relatively happy and relaxed, although a few still had multiple final projects to complete. Much ice cream was consumed. The pear chardonnay sorbet was not consumed, but I have to say, it was outstanding (it came home and disappeared stunningly quickly). It was a good end to the course!

The final

For the curious, here is the final exam. I thought it was pretty tough; it was certainly time consuming to grade (it took me the better part of a week to grade 45 exams -- I'm guessing over an hour per exam). The students did exceptionally well -- a typical Margo-exam ends up with a median around 67%; this one had a median and mean over 80%!

The first problem was a design exercise and those are notoriously difficult to grade; after two days of grading I wondered why I continued to give these kinds of questions. Then a colleague, Kryzstof Gajos, explained how we graded his final exam, and I am excited to contemplate how I can apply this technique. I've invited him to write a guest entry on the topic, but in the meantime, here is my understanding.

The course he was teaching is called CS 179: Design of Usable Interactive Systems. It is very much a course all about design. So for the final exam, he split the period into two parts. During the first part, students took the (written) exam using a "uniquely" colored pen (provided by Professor Gajos). Then, he collected the pens and the class collectively graded (their own) exams. Thus, in real time, the class discussed the problems, the supposedly right answers, alternative answers, etc. When there was ambiguity, they discussed it. Afterwards, he collected the exams, had the TFs check that the self-grading was accurate and he was done.

This was pure brilliance! I'm not saying that because it reduces grading time (which it does), but because it turns a purely summative evaluation process and makes it partially formative. I try to do this when I grade exams -- I essentially engage in a typewritten discussion about their answers (which is one reason exams take so long to grade). I always have second thoughts about this, because I know that students merely search for the final number and ignore everything I write. Or so I thought (more on this later). The idea of discussing the exam right after they've finished it and being able to address confusion immediately is overwhelmingly appealing to me. It's not entirely clear how to apply this to my exam -- I like pushing students to think about complex issues for which mulling the ideas and questions over is useful (this is why I like the takehome exam format). I don't know how I'd fit both the testing and the grading into a standard 3-hour test slot. If I stick with the 24-hour format, then I'd have to make the exam be, say, a 20 hour exam with a scheduled 2-hour class which sounds like a logistic nightmare. I'm not sure what I'm going to do here, but I see further experimentation in my future.

In addition to a design question, I asked people to read a research paper ( the Barrelfish SOSP paper), and then I asked them questions on it. I'm really looking forward to having some of these students in my graduate OS class, because the high bar they set for a system is quite interesting. Many were accepting of a prototype, but a surprising number took a more business perspective, while perhaps not appropriate for a research paper, indicated to me a much better sense of how the world works than many tech-savvy people are. I found it fascinating.

In another question, I asked them to respond to a (rather poor) technical suggestion, but I asked them to do it in the context of an email to an engineer who worked for them (I put the students in the role of being the project architect). I was quite impressed with the care most students took in crafting a reply that was both technically correct as well as polite.

The post final

Although I write fairly long comments on my students' exams, I know deep inside that they never read them, and yet I continue to do it, because I know that there is the potential for learning there. This year, I was pleasantly surprised -- for the first time in twenty years, I had a couple of people engage with me after the exam to discuss answers. They weren't looking for points but were instead, trying to make sure they understood what a right answer to a few questions would look like. In one case, a student wrote up about 5-6 paragraphs as an answer to one problem to make sure that the student had a complete grasp on the answer. I was (pleasantly) astonished. While I can't make any causal statements between new pedagogy and this behavior, I could certainly believe that because I am much more closely engaged with students, they felt more comfortable doing this. In any case, I was quite pleased.

The end

And so, one woman's adventure with flipping comes to an end. I'm looking forward to crunching data, and I'll certainly post here if/when I find something interesting to say. In the meantime, here are my parting thoughts.

• It's good for an old dog to learn new tricks.
• Flipping lets me spend time with those students for whom the material is challenging.
• Learning takes place by doing, not by listening to me.
• TF engagement is critical.
• It takes a lot of effort to come up with effective in-class work.
• Pre class web forms are AWESOME. They let me engage with students in an entirely different way and to gather lots of interesting data.
• CS161 is even more time intensive than I thought.
• It would be useful to help students learn what it really means to design something.
• Flipping is a great equalizer when students enter with different experience levels or exposure to different topics.
• Fully integrated and coordinated materials take real effort but pay off tremendously.

Flip N-1

The penulatimate week of the semester was a busy one! I have some fun data on how the students view assignments, some experience with the partially-flipped classroom, an interesting discussion of a flipped exam, and finally the totally awesome creativity of my students as expressed via T-Shirt designs.

The Pain/Gain Scale

One of our former PhD students is now on the faculty at Swarthmore and he suggested to me the pain/gain scale as a way to determine if the degree of difficulty in assignments was perceived to be worth it. This seemed like a fine idea, so I polled students on the two major assignments completed so far, asking them to rate on a scale of 1-5 the amount of pain the assignment caused and the amount of gain they derived. The results are fascinating.

Here is the histogram of the responses:

At first I thought that Assignment 3 was really nice correlated, but then I calculated the ratio for each student and graphed that -- it tells a different story:

While most people found the ratio about 1:1, there were some who clearly suffered and others who had a blast. I have not done further analysis, correlating these ratings with how well groups did, but I found it interesting nonetheless.

The Partially Flipped Class

The astute reader will have noticed that while upholding my deal that I will not make students prepare for class while they are also implementing processes, building a VM system, or making a file system recoverable, it's been difficult to maintain the energy and enthusiasm of the flipped classroom. As I entered the homestretch, I decided to try an experiment with what I am calling the partially flipped classroom. I take my lecture notes and I break them into two parts -- a short intro (6-8 slides) and the rest (10-20 slides on technical content). I present the intro and then I dispatch the class for 15-20 minutes deriving from first principles some of the challenging aspects of the particular topic and approaches for addressing those aspects. For example, on Tuesday I was teaching virtualization. Now that they had built major pieces of an operating system and become intimate with other parts of the OS, I let them figure out what the big problems were in building a virtual machine-based environment. The groups each came up with excellent lists, which we then pooled. When this was all done, we'd covered much of the material in the rest of the slide deck. So, I was able to breeze through the rest of the deck relatively quickly and I knew that they had a much more complete picture of the topics, because they had largely derived them themselves. It felt very good. I repeated the process on Thursday with security. I introduce the three A's of security: Authentication, Authorization, and Access Control and then let them play around with identifying what can go wrong if you fail to address each aspect properly and then proposing approaches to solving it. This week, we'll be able to breeze through my slides on the topic relatively quickly, because most of the ideas came up in discussion. That will leave us time to talk about a few real world exploits.

I think this is the approach I want to try for all the material that I had been teaching "the old way." I'm pretty sure that with some careful thought I can make it work and we may be able to maintain a higher level of energy and engagement during the roughest parts of the semester. We shall see!

The Flipped Exam

Thanks to the wonders of Facebook and my friend Jill Levien, I was introduced to the idea of a Flipped Exam. Now, I don't teach game theory and I'm not entirely sure how this would work for my class, but I found it intriguing, so I posted it to our class discussion board with the directions "Read/Discuss." And my fabulous students engaged!

Student1: We should have such a final exam: the entire class: write
as much as possible of an operating system in 24 hours together.
editdelete

Student2: While I do think there is a place for individual examinations,
the current educational system overvalues such tests. My basic
understanding of the "real world" is that most projects of any real
significance are done in teams, be it research, commercial products,
etc. Sure, there have been cases of lone wolfs that create paradigm
shifts or fantastic projects (and this should be encouraged as
well!), but teamwork is ultimately a skill that should be encouraged,
not subdued. (24 hours might be a bit short to get much functionality
done on an OS even with a full class of people, but I certainly
wouldn't mind a collaborative written final).

Student3: Synchronizing >40 people would be so much fun...

Student4: I really like that idea. It will be a fun, collaborative
experience, and we'll end up synthesizing the entire semester
together into one glorious product.

Student5: This idea was the first thing I thought about as well. I
think it would be fun, maybe not necessarily writing a whole new
operating system, but writing another subsystem for OS/161.

TF1: Rob Bowden: Networking!!

Student5: Indeed that would be fun.

Student6: so punny

Student7: You get a synchro bug! And you get a synchro bug! Everybody
gets a synchro bug!

Student8: I find this much more reflective of how the world actually
works and I think it reminds people that the best answer is 99% of
the time not produced in solitude.

I'll second Student2's final suggestion as well.

Student9: If it's a coding assignment, maybe we'd need (want) groups
of a smaller size. 45 people can't all be coding at the same time,
so it seems as if the exercise would likely devolve into "Okay, you
two/three/four code, we'll just watch...and write a DesDoc? And,
uh, run tests!"

What about five partitions of nine, sorted day-of? You've got 24
hours to do what you can on [subsystem], working with some, all,
or none of your tablemates. Coordinate sleep, food, and synchronize
your watches...here's an assignment spec, go!

Right now I think I'm still going with the individual exam, but I'll definitely have to think about the concept of collaborative exams for the future. I am glad the class (or at least a subset of it) thinks that working together would be fun.

T shirt Designs

Even in the midst of a pretty heavy workload, my students know how to have fun. Check out the T-shirt designs on our home page. I'll let you know which design won after the T-shirts have been delivered.

Next: Flipping Over (May 24, 2013)

Anxiously Flipped

It is 4:57 on Marathon Monday, and by the time you read this, I'm sure you all know what transpired today in Boston at the finish line of the Boston Marathon. I am grateful to be safely home and am at my keyboard waiting for all my students to check in. As Harvard has classes today, I am optimistic that my students were all in Cambridge, safely out of harm's way. Even so, I'll be happier when I see their messages. If only everyone else would be so lucky.

I figured that blogging might be a distraction from the day's events, but nonetheless, my suspicion is that this will be short and perhaps scattered.

It was a rough week to be a CS161 student. The virtual memory assignment was due on Friday and it is a particularly devilish assignment -- the number of lines of code to write is not huge, but getting the synchronization correct is just downright hard. This sets the students up for a lot of late night debugging, perhaps an all-nighter, and then perhaps a couple of late days. This has all played out reliably over the past many years.

So, this week's status has much less to do with flipping and much more to do with CS161, virtual memory, and why anyone would put themselves through this. For your reading pleasure, I bring to you a Facebook discussion that took place after I posted a note about how guilty I felt coming in at 8:00 AM and finding my students (surprisingly happily) working away, having been up all night. Let me just say that I never looked that happy after an all-nighter.

My original post: There is nothing quite so guilt-inducing as walking into your office at 8:00 am and seeing your students sitting in the lounge working on your problem set after having been working on it all night. Oh wait -- there is -- seeing multiple groups later that day around 4:00 PM -- all of whom have been up all night and are still working. Many of them now have operating systems that mostly support virtual memory, though!

In the following, I have converted names to initials, to provide some shred of anonymity.

• GK: That last bit, "mostly support virtual memory," reminded me of this and this.
• MO: that's guilt-inducing? I thought that's what you live for!
• RH: And yet, it didn't keep you from giving them the assignment in the first place. Hmm! Actually, IIRC, that was the easy assignment. It was the stupid filesystem one that almost killed me. I wonder if these assignments would still seem as hard today as they did 15+ years ago when I did them (am I really that old?).
• GK: Tell them that in 24 hours Andy Sudduth finished his operating system, finished putting together his HeathKit computer (this was in the early-to-mid 1980s), wrote a full screen editor, and then wrote a paper due the next day in his editor on the computer he built running the OS he wrote. Or, you can tell them what I try to tell myself—start sooner. Editorial note: Yes, Andy Sudduth, Harvard legend and Olympic rower is also a graduate of CS161
• Me: We've tried many, many things over the years to attempt to make the problem sets less time consuming, but at the end of the day, learning to build and debug asynchronous, multi-threaded programs is just plain hard. And we continue to get the feedback, even years later, that the time is well spent. I have an awesome class of 45 who, although exhausted, still seem deeply happy with what they are doing.
• GK: And since I mentioned Andy, rest his soul, he also loved that course.
• PA: I have fond memories of programming such things when using an ascii terminal to an under-powered VAX11/750 running BSD4.2 with it crashing every now and again... your students should be happy their development environment is pretty stable!
• RH: @Margo: I agree. It was a good class. It retains, however, the distinction of being the only 40-hour-a-week class I ever took. Second place was about half that. @GK: If those students are anything like me, not starting soon enough wasn't the problem.
• MO: it's no fun without an all-nighter once in a while
• MO: Of course, I never took the course, just had the enjoyment of watching BF and others suffer through it
• MW: Wow, 45? That's awesome.
• PR: It's a public service. Think of of the trouble those students could be getting into if they weren't locked up building an OS.
• NM: I wonder how many techies at the likes of Google, Facebook, etc. would still get a chill down their spine at the mere mention of "assignment 3"?
• DK: I still fondly remember our all-nighters in CS161 (with CY). Professor Hsu said we built the class's most elegant OS (everything was based on a common semaphore implementation). And it always ran for at *least* 30 seconds before crashing.
• CY: I remember the class being a 9 to 5 affair. PM to AM, as that was the only time M, D, and I had in common. And I fear that the elegant semaphores were woefully slow--the guys that used atomic ops to access the priority queue were twice as fast as our version where the semaphores also managed priorities.
• DK: I think that was also the class where we wondered "what happens if you tell the unix shell while (1) fork() ?" and took down the department compute server for the night.
• CY: I think it was only microvax-6.husc.harvard.edu, out of of a fleet of 10 or so microvaxen, and not the file server (thank goodness). The Magican's Apprentice moment was priceless, though, as we tried and failed to kill the parent process and started getting "no more processes" messages from our other shells. The next morning, the sysadmins were more worried that we were doing some important computation than about our abuse of the machine--they just power cycled it and everything returned to normal.
• CY: Actually, the real thing I should say about Prof. Hsu's CS161/261 class is that, of all the hacking classes I took at Harvard, it was by far the most useful in the rest of my career. I think it was the construction of synchronization primitives in a raw environment and figuring out how to debug code built on top of those primitives--there's nothing like it for combining power and danger, and for whatever reason being able to build such things remains a rare skill.
• DK: I think the "whatever reason" is that we have done such a good job of creating layers that shield students from the "raw environment"---students building a web application in Django have no idea how many layers of complexity are hiding between them and the hardware, and wouldn't know what to do down there. The hard question is whether this is a good thing or bad----given that we have already built the layers, do we want to force every student to really understand them, or is it enough for them to use them?
• And to make my colleague MM happy, I won't cut this one out DK: As for most useful classes, I've got to flag Umesh Vazirani's CS124, at least to the extent that "useful" means "determined where I am now".

And to top it all off -- this week's picture, straight from China: Tao Stein's students at midnight working on their ray tracer.

Next: Flipped Out (April 22, 2013)

Missing Flipping

Since I'm back in more conventional lecturing, there isn't much newsworthy to report, so I want to highlight just two things.

First, I recently learned that one of my students is blogging the course! I was thrilled when she said I could link to her blog. She is far more poetic than I, and I love reading her entries.

Second, I was chatting with a colleague recently who said that she couldn't tell whether I liked flipping or not. I thought I had been making that clear, but just in case, the point isn't coming across. I'm going to rant for a bit on just how excited I am about flipping.

I am completely sold on the flipped classroom. I will talk at great length to anyone who will listen; I recently used flipping as the centerpiece in the session I did for our teaching practicum; I have yet to hear a compelling argument for why you would not want to flip (as long as you could figure out space issues for a large class). I believe that I have covered all the reasons I am so enthusiastic about it, but just to put them all in one place:

• The teaching staff can focus time and energy on those students who need it the most rather than those who are most vocal.
• Pre-class work gives me concrete data on how students are doing -- what they know, what confuses them, what they don't know.
• Because the pre-class work is built into the class structure, I have a mechanism to obtain immediate feedback on most everything. I believe you could do this in a more conventional class as well, but it falls out naturally here.
• The pre-class work also gives me a way of staying connected with each student. I regularly check in on how partnerships are doing. We had one pair on the brink of divorce, but it appears to have been salvaged. I will point out that I have never taught this course without having at least one divorce, and it currently appears that we will have no divorces, even though we have more students than we've had in a decade.
• The physicists demonstrated that peer instruction works, and this confirms it. The students learn a lot from each other.
• Flipping can be the great equalizer -- if students already know half the material, they can skip the audio decks on those topics rather than having to sit through a lecture on them, just to get what is in the second half of that lecture.
• Preparing the coordinated materials makes me think much more deeply about what I'm teaching, how I'm teaching, and why I'm teaching. The end product is therefore better thought out.
• I've discovered that one becomes very sloppy while lecturing. You can walk into a class with lecture notes and wing it. However, I cannot wing recording an audio track. Because I can revise each slide track by itself, I will re-record until I have a very crisp, tight, clear explanation. I think this is a big win.

All that said, flipping, like any other mode of teaching, can be done badly. I've certainly experienced that. I believe that the work to be done outside of class, the pre-class quizzes, and the in-class work must be tightly coordinated. I also believe that the instructional staff needs to be fully engaged during class.

Next: Anxiously Flipped (April 15, 2013)

Inadvertent Flip

We're back after spring break, and it does appear that most of my students took a much-needed break. We kicked off our first week back with our second peer design review and then on Thursday we dug into file systems. So, today's post will revolve around two topics: observations from the peer design review and a discussion about class participation.

Peer Design Review

This was our second peer design review and I was struck by two things. First, it seemed that it took longer for the students to read through the design doc of their peer group. I speculated that perhaps the students had started writing more in-depth detailed designs, so I decided to ask about that in the week's web work (which are just short surveys at this point). Turns out that this was not what I was seeing -- about half the class claimed that the A3 design they reviewed was about the same quality as the A2 design they reviewed. And the other half were split as to which was better (there was a small tilt towards the A3 designs being better, but nothing huge).

The second thing I noticed was an overall spirit coming out of the discussions. They seemed genuinely happy to be talking about fault handling and page allocation. They also seemed surprised that when they asked the staff certain questions, they got multiple answers, "I did it this way." or "Oh yeah, I didn't do it that way, I did it some other way." I thought this was good -- there are rarely right or wrong answers in design but instead a set of tradeoffs to be considered. And seeing that the staff didn't necessarily agree but could engage in a discussion of tradeoffs and relative merits was valuable in and of itself.

Participation

I have always graded on class participation, believing all the research indicating that people learn better when they are engaged. I know that class participation is difficult for some, and I always let students know that they can earn participation points by sending email before or after class to discuss things that they found either challenging or interesting. At the same time, I tell those students that my goal is that by the end of the semester they do feel comfortable speaking up in class. And nearly every semester, they get there, and it's a wonderful thing for all of us.

Anyway, I always have students who never speak, never email, and never say anything about it. I've come to accept that as normal. Now, this year, I figured that participation grades were easy to come by because I consider web work and small group work in class part of participation. So I didn't worry too much about even my quietest students, because as long as they were in class, there was no way for them not to participate. Imagine my surprise when in the very same week, two of my students brought up the topic of participation. I was shocked. I'm convinced that this never would have happened if I'd been teaching this as a conventional lecture, but somehow these students, who were doing everything asked of them, somehow felt that they should be engaging more.

I assured both of them that from a grade standpoint everything was well, but I used it as an opportunity to engage in the greater discussion about how to participate, what I could do to make it easier, why participation was a good thing, etc. I'm curious to see what happens, but I was so (pleasantly) surprised to be able to engage in these discussions that I had to write about it.

By the way ...

I just want to say, "My teaching staff Rocks!"

Next: Missing Flipping (April 8, 2013)

Testing and Flipping

This was our last week before Spring break, which means two things: First, there will be no posting next week (although it might be the perfect time to slip in a non-teaching related entry) and second, this was the week of the midterm.

As I watched my students taking the midterm I was quite literally awestruck. Before me sat a room full of incredibly talented students, and I get the privilege of being part of their educational experience. The only other time I've been struck with a similar feeling was when I used to teach our (then) 300-person introductory computer science course (it's now about 750 students and growing strong thanks to the amazingly talented David Malan).

But this was different. These students have been working incredibly hard for the past three weeks getting their operating systems to fork and exec processes. A quick look at the data suggests that a typical student spent almost sixty hours working on the assignment over those three weeks. Yup, that's twenty hours a week for one of four courses. Ouch. I guess that explains the claims of students spending 60 hours weeks on this course -- historically there were always students who didn't do anything the first couple of weeks and then tried to do it all the last week. Things seemed a bit better this year with many people making steady progress over the three weeks.

Anyway, back to the exam. Having loaned my laptop to a student who had somehow missed the discussion about taking the test online, I had nothing to do other than watch them. There they were, all intently focused on the exam, typing, thinking, shuffling through slides. It was an open notes, open book, open course materials (but not open Internet) exam. I appreciated that they asked if they could read the course Q&A site during the exam -- I did draw the line there, even though they all certainly seemed to understand that posting questions was not going to be on the agenda. Towards the beginning of the test, there was much shuffling through materials, but as the test progressed, there was less. My theory has always been that I can make tests open book, etc., so long as I write questions that require synthesizing information so that the materials aren't actually that useful. There were a couple of questions where a glance at a set of slides would prove useful, but in most cases, there simply weren't places they could look for an easy answer, unless they already had a pretty good idea about the question.

I was quite curious to see the results. It's not possible to run a real apples to apples comparison beacuse a) this class is twice as big as it was two years ago, b) it's a different exam, and c) it's a different way of teaching. So, any results are open to interpretation. The results are surprising -- the distribution is almost identical to that two years ago. However, there were no truly bad grades -- last time, 2 of 23 students had grades on the midterm that were cause for alarm; this year, there were no grades that worried me (it appears that grades that worry me are those more than 2 standard deviations below the mean).

I'm pretty sure I cannot conclude anything from this. So, we'll have to wait until the assignments are graded. In this case, the assignment is pretty much identical (I saw pretty much because we asked different code reading questions, but ideally I can dig up the grade breakdown and remove those). Time will tell.

Next: Inadvertent Flip (April 1, 2013)

Half Flip

It's the end of week six -- almost half way through the semester and this week was a perfect way to celebrate that -- half flipped, half not flipped. On Tuesday I gave a fairly conventional lecture. My gut instinct is that the class is a tad more interactive than past years, but I can't attribute too much to that since it's also larger and we're in a different space, and both of those things might contribute.

Thursday was our annual midterm review. In the past I've simply gone over an exam in class or broken the class into fairly large groups and had them make up questions, present the questions, and then answer them. This time I let them submit questions as web work before class, promising that I would, in fact, use some good ones on the exam (having now written the exam, I have selected a few -- I did have a moral dilemma -- one student suggested a nice question, but answered it incorrectly -- I really didn't want to use a student's question and have that student get it wrong ...).

In class, I let them work at tables (groups of 3-5) on sets of problems and then we came together to talk about them as a class. Since many of my exam questions have multiple answers, it provided a good opportunity for both table-wide and class-wide discussion. I guess we'll see how it all works out next week.

I have noticed one other difference between this year and previous years. My staff seems to be thinking a lot more about teaching -- what we teach, how we teach it, etc. It's hard to attribute that to any one thing, because there are so many variables, but I do think that there is something about the setup that gives us more opportunity to think critically about what we're doing. Also, the fact that we have some flexibiity in how we present material means that we can be facile at adapting to the students, what's working and what's not. This week's discussion at staff meeting revolved around design -- how do we teach it? Why don't we teach more of it? What can we do now to do a better job? I have such respect for and appreciation of my teaching fellows who engage wholeheartedly in such discussions -- they are close enough to having learned the material that they remember what is hard and they are enough past it to know what skills matter. We're still in the midst of this discussion -- I'll let you know how it works out!

Next: Flipping and Testing (March 18, 2013)

Unflipped!

We've entered that time of the semester when the students are busily creating user level processes in their very own operating systems. It is both exhilarating and exhausting. Due to that exhausting part, this is the part of the course where I promised not to make them do pre-class work -- there would be no videos to view and no web work (other than quick surveys about how much time they are spending). That means that, for the most part, I have had to revert to a more traditional class structure -- I talk and call on people and we try to collectively learn stuff. It feels dull; it feels unsatisfying; it feels as though students are not engaged. I am looking forward to polling them about this class structure so we can decide how to move forward during the next several assignments.

Since we're not flipped, I have little novel pedagogy to talk about nor do I feel the exhilaration I've felt throughout most of the semester (and any of you who have run into me and dared ask about the course know that I can now babble incessantly about how fantastic flipping is). So, today's entry is about two things: how it feels to be lecturing again and thoughts on what I would do if I had 250 students instead of 50.

The Traditional Lecture

It sure does take less time to prepare for class! Once I finish class notes, I have finished class notes. I don't have to think up pre-class activities; I don't have to think up in-class activities; I do spend a bit more time working through the notes, deciding when I can engage the class and which activities can be converted into class exercises.

As has historically been the case, I find myself interacting with about 20% of the class, instead of all of them. This is rather disappointing. I coax, I tease, I cajole, but some people just don't want to speak up in class. I do find it effective to ask for a raise of hands to vote on whether answers are correct or not and I seem to get better participation than I have in the past, and my sense is that even when I'm trying to extract thoughtful answers from people, I have a slighly larger fraction of the class engaged, but it's nowhere near the 100% that are engaged when the students are completing in-class work.

I also have found it effective to try to convert some of the open-ended questions I typically ask into exercises that the students can complete in groups. Even if it only takes a minute or two, it means that more people are engaged. It is this last tidbit that got me thinking about our next topic ...

Flipping 250 Students

A few of my colleagues have indicated that they have been thinking of how to flip significantly larger courses and it poses an interesting question. What would I do if I were teaching CS51, which is a heavy-duty programming class and has roughly 250 students?

Classroom space is the first obstacle. I love teaching in our new state-of-the-art classroom that has reconfigurable, mobile tables, traveling whiteboards, screens on both ends of the classroom, etc. However, it holds only 54 students, and even if you could build a bigger one, I think it would rapidly become sufficiently cavernous that you'd lose any semblance of a class. So, I would constrain my thinking to what would work for a more traditional lecture hall.

Since the students won't be able to cluster around tables, I'd probably try to use some kind of online shared whiteboard-like tool. That way students could bring laptops and work together in groups of 2-4. I would also want some way to do real-time data collection. I don't think you need any special clickers -- I would see if Google Forms work well enough in real time that people could submit answers and I could see the overall statistical picture of how students are answering.

The physical layout is going to make it difficult for the teaching staff to circulate -- you can get to the edges of rows, but getting into the middle would be tricky. I'm not entire sure how to deal with that -- I suppose the staff could join the online discussion, but it's not the same as interacting with the students directly. This would seem to be one of the biggest obstacles -- I just can't see the teaching staff climbing over students to get into the rows; having the students get out of the rows to talk to the staff doesn't sound better. I'm also not completely sure how the noise level is going to play out in a room with that many students. You really want them to be able to talk to one another, but a room of 50 sounds pretty chatty; I'm not sure how loud a room of 250 will sound.

So, those are my thoughts, but I think that the best thing would be to run a experiment. Perhaps if one of my colleagues invited me to guest lecture in his class, we could prep a single class and give it a try!

Next: Half Flip (March 9, 2013)

Addicted to Flipping (week 4)

In theory I was supposed to return to regular lecturing this week, but it didn't happen. It might have to happen this week, but right now, I am addicted to flip (and I have a sense that my students are too).

Tuesday I had scheduled for peer design reviews. Let me tell you a bit about how the course works, so that this all makes sense. The three meaty assignments of the course ask students to 1) implement user processes (fork, exec, and a handful of other useful system calls, etc), 2) add virtual memory, and 3) make a simple file system recoverable by adding logging to it. The students work in pairs and are left to both design and implement solutions themselves. We ask them to first submit a design document. The teaching fellows review the design documents carefully and then interview each team, giving useful advice, pushing them on how much they have really thought about what they need to do, clarifying any misunderstandings, and otherwise acting a bit like a project manager.

Historically, design documents vary widely in quality. A few are always nicely done, thorough, well thought out, and complete. Many are usually superficial, because the students are still struggling to wrap their heads around what they are supposed to do. TF feedback is invaluable.

So, this year, before handing the designs in to the teaching fellows, we scheduled in-class, peer design reviews. Each team met with one other team and exchanged designs and then spent an hour discussing and questioning each other on the design. The questions and discussions we heard sounded quite good -- people were asking all the right questions and the teams were pushing each other in just the right way.

At the end of the class, one student made a point to say that he thought the class had been incredibly useful. We will be getting the final designs this evening, so I won't know until next week whether this resulted in qualitatively better designs, but I remain optimistic.

But I suppose my real addiction came out Thursday. Since they are now deeply enmeshed in Assignment 2, as part of my contract, I will not ask them to prep before class. In general, I assumed that meant I would return to lecturing, but as I surveyed my notes on various advanced scheduling algorithms, I couldn't quite see me or the class getting excited by a lecture on this stuff. So, I took a risk.

I prepared four presentations on some scheduling algorithms (a Solaris style Multi-level Feedback Queue scheduler, the Linux completely fair scheduler, a BSD-style fairshare scheduler, and a lottery scheduler). Then I created six roles: four engineers, each of which is partial to one of the schedulers, one product manager and one engineering manager. Each role had some "private" information and the roles and information were on pieces of paper stuck in paper cups, 6 to a table. Students formed groups of 6, selected a role from the cup and then spent about an hour in a design discussion. Given their target platform (which only the product manager started out knowing), they had to select a suitable scheduler.

My goal was that rather than having me go through the plusses and minuses of each approach, they would be forced to compare and contrast and figure out when each one was good/bad. Then each team presented their target platform and their selection, with justification. We wandered around and answered questions and also assumed some other roles: CEO who has an opinion about everything, but isn't technical, VP of marketing who fundamentally distrusts engineers, and the head of QA who would be responsible for testing their systems.

Once again, it's difficult to tell, but my sense is that they covered the important points and each has a deeper, more gut-level understanding of the various approaches. Only time will tell!

Next: Unflipped! (March 4, 2013)

Not Flipping Out (week 3)

We've just completed our third week of the semester and my flipping experiment continues. In honor of flipping the class, we will now refer to CS161 as CS191.

I'm still a fan.

There were no enormous disasters this week nor were there any sudden breakthroughs (I fully expect that simply due to this new course structure, one of my students will inadvertently do something to win him/herself a Turing award, but not quite this week.)

So, this week I will write about four happy and unintended consequences of this new arrangement.

1. Flipping as an Equalizer

Students enter courses with different levels of expertise and experience. This is always a challenge as some students constantly feel behind and others sometimes feel bored (although rarely do students feel bored while trying to get OS/161 to fork processes). With the flipped arrangement, I can break up the material into distinct topical areas with videos per topical area, and students can pick and choose which ones they need to watch. They can check out the web work and see which questions they know without viewing anything and which ones indicate they may need to view a video or do some more reading. My sense is that this acts as an equalizer. It's not perfect, but it's definitely better than a more traditional lecture where at least one student is lost and another is bored.

2. Maximizing Teaching Utility

I feel like an idiot for not having realized this before, but flipping lets instructors spend time with the students who can benefit most from that time. When I try to run an interactive lecture, I typically end up engaging with the students who are most comfortable and most expert. After all, they are the ones most willing to speak up in class. They are also usually the ones most willing to ask questions. Sure, I can look at the class and try to detect overall class confusion, but do I always catch the student who is really confused? I think not.

In contrast, when I and my teaching staff^* wander around the room, we spend time with the students who are struggling or who have questions. We check on groups and cheer on those who not only have fork and exec working, but have implemented job control, backgrounding, programmatic scripting, and twelve other features in the past ten minutes. Yes, we're excited for the students who excel, but we can be more useful in making sure that all the students are succeeding. And by and large, at the end of the session, every student has experienced some form of success. I am pretty convinced that few students walk out of a normal class feeling successful. They may feel like they were in a good lecture; they may have enjoyed it; but I don't think they feel that they were personally successful. In contrast, getting your shell to fork and exec, proving a scheduler optimal, or deriving a good scheduling routine can let you feel like you've actually accomplished something.

3. And then I travel ...

As much as I hate it, I do sometimes have to travel during the semester and miss classes. While I have talented colleagues and wonderful teaching staff who fill in for me on those occassions, I don't like it. This February is the worst -- I have three trips I have to make. Under normal circumstances I should have missed four classes, but I couldn't do that so I jiggered the trips so I will only miss two (which means I missed NetApp University day for the first time, which made me sad).

All that said, being away is not nearly as disconcerting as it is under normal circumstances. First, I can check on the web work so I have first hand knowledge of how everyone is doing. Second, I have already prepared the material I wanted to present, so that isn't very different. Third, although I cannot wander around class, I have four or five teaching staff fully engaged in the class time activity and they are wandering around talking with students and getting firsthand feedback on how things are going.

Normally, when I've missed a class and I ask how things went, I get something like, "I think it went OK." This is a truly honest reply, because someone giving a guest lecture has very little feedback on how things actually went. This time, however, I got, "Very well. I guess main things I noted:

1. People seemed good conceptually; questions I got were insightful.
2. People had a lot of trouble with the proof, so I eventually told them to move on to the design problem and come back to the proof if they weren't done.
3. I had time for one group to present their scheduler idea and it was essentially good (a min-heap with priority proportional to sleep time).
4. I had time to show the bounded priority queue idea and explain that the distribution of jobs is usually thought of as multinomial. (The group that came up with the min-heap scheduler included a math student who was trying to show it was somehow optimal for a power law job distribution, which was pretty neat).
5. I think some people may have been working on A1 in class, but I'm not sure that's bad."

I have a much better sense of what was covered, how students are doing, etc. Yes, it took more work before I left, but it was entirely worthwhile.

4. My Teaching Fellows seem more engaged and happier

^* At Harvard, teaching assistants are called Teaching Fellows. This is a moniker that arose when most such people were graduate students and the stipends they received were part of their fellowship. Technically, when undergraduates assume these roles, they are teaching assistants and not teaching fellows, but drawing such distinctions would be silly, so the culture is that we call all such people Teaching Fellows, or more colloquially, TFs. Apologies for not clarifying that earlier.

In a conventional course, the TFs are pretty disengaged from lecture. I usually want them to attend (mostly to fix things I botch up), but since they've all taken the course before, they spend much of class tuned out and doing their own thing (defeating the purpose of my having them here in the first place). However, in the current setup, the TFs are fully engaged. They are wandering around talking to students, fixing things, and actually teaching. Since most of them take these jobs because they enjoy that sort of thing, they are spending more time doing the part they like (let's face it, none of us are that excited about the grading part). In general, they seem happier to me and more interested in what's going on in the course.

And, at least to me, they say that the class time is fun. This too strikes me as a good thing.

Next: Addicted to flipping (February 21, 2013)

Flipped Again (Week 2)

Last week I was full of euphoria; this week not so much. I'll cut to the chase before diving into details. First, teaching this way takes at least three times as much preparation as teaching "the regular way." I still think it's worth it, but I can tell that it's going to take its toll. Second, in a programming course, preparing pre-class work and in-class work is a detail-oriented process, and if it goes wrong, it can go badly wrong. Third, I am hoping that full transparency, honesty, and a lot of humility will help to mitigate the disasters that can happen as a result of the previous item.

Part One: Time Intensity

Regardless of how I teach, I try to prepare thoroughly. When I lecture traditionally, I hand out notes, so students have the outline of what we're covering, but I leave a lot of blank space that I try to fill in collaboratively with the class. However, I always have the main points jotted down on my notes, so I make sure to cover the things I want to cover. After class, when I discover errors or things that didn't go well, I either fix the notes then and there or leave myself notes for next time. In either case, my notes and lectures are constantly evolving and changing.

So, how does that kind of preparation translate into my current situation? First, taking last year's notes, updating them, and then preparing the audio track requires at least a factor of two more time, perhaps even more now that I'm thinking deeply about it. Applying the same fixes I would have applied were I teaching conventionally takes about the same amount of time it would have. But then I start recording audio tracks. In my case, I'm using discrete audio files per slide, attaching them to the powerpoint, and then converting that powerpoint deck to a movie. The logistics of all this are tedious and take time, but that's not interesting (e.g., the PPTX->movie conversion really only works well using software that runs only on Windows; it produces enormous files, which I then translate using a different tool; these large files get moved around, etc).

The more interesting is what goes into preparing the audio bits. Since students will be listening to these on their own, they don't have the opportunity to interrupt and ask clarifying questions. We do have an interactive message board, and the students are taking good advantage of it, and the TFs and I are working hard to be responsive, but it's not the same as saying, "Excuse me, I didn't understand that." OK, few students ever actually say that in class, but when you can see them, you can frequently figure out that they are thinking that. In lieu of that, I think very carefully about what I want to say, how I want to say it, and then I record. I'd say right now about one in three times I am happy with my first take. One in three times I need a second take. One in three times I do many, many takes. So far, the videos have mostly come in around 30 minutes, so we're talking a couple of hours when you add in recording with incorporating the audio track, setting options, fixing things, etc.

But once I've completed the audio track, then I can really begin. Next I think about what I want them to take away from the video and I translate that into pre-class work. I think I am posing somewhat more challenging pre-class questions than one normally associates with this task, because I use those results to help me identify what issues are really confusing people. (I spend an hour or two in the morning before lecture reviewing answers, analyzing responses to the various questions, discussing them with my staff, and figuring out whether I want to a) simply post answers, b) go over problems in class, or c) do nothing.) In any case, I spend somewhere between 30 and 60 minutes thinking about and writing pre-class work.

Then I begin working on the in-class component. In our case, this involves writing code. Writing code always (always, always) takes longer than you expect. Testing is key. However, since my pedagogical thinking evolves as I am working through the assignment, sometimes I don't always use the practices. This brings me to item two on today's list.

When Disaster Happens

We had no fewer than four different types of disasters happen all in the span of a single 90 minute class (of which 30 minutes was consumed discussing pre-class work). There are many things to learn from this experience, so I'll walk you through what happened in potentially gory detail.

1. Pre-class work

It turns out that unless students were clairvoyant and could read my mind, there was much ambiguity in the questions as I wrote them. Both TF feedback and the analyzed data supported that claim. So I took the first 30 minutes of class to go through the questions and discuss the different interpretations and how those interpretations led to different answers. My assessment is that while it didn't feel good to be me, the end result was actually pedagogically constructive. We ended up talking about a number of important concepts and assumptions as a group, and I think we raised issues that, in past years, never surface, are never addressed, and manifest in difficult-to-debug code later in the semester. It will be difficult to do any kind of hard empirical analysis of this (although if people have ideas, I'm all ears), but my sense is that we had a deeper discussion about synchronization than typically happens.

2. Preparing for in-class work

After that, we turned to the class work. I had prepared the exercises as a separate branch, with the intention that they could play with it in class, and it would not in any way interfere with their own work, and afterwards they could either keep it or toss it without any effect. Great idea in theory. In practice, due to a combination of miscommunication, my own experience with the particular source code control system we're using (there were good reasons to change, but it's not one I've used extensively), and pretesting the process on a tree that was not identical to what the student's had, we ended up having them execute a command that, well, um, kind of messed up their tree.

3. Dealing with the in-class disaster, or "Another Disaster in the Making"

When then insued was sheer insanity. Over the course of the next 15 minutes, we frantically proposed multiple different ways of fixing people's trees. The TFs, students, everyone had an opinion, and we kept posting them. This was just dumb. We should have stayed calm, figured it out, and then dealt with it. But no, we freaked out -- all of us!

Finally, I went around the room and checked on every person to make sure that they had a working tree. That seemed like a good idea. Hoewver, then the fun really began.

4. The Crowning Touch

As they started working on the problems, they discovered truly, horrifically idiotic bugs in the code. How did that happen? I really tested things. I really did. Honest.

Ah yes, I'd done a couple of those last minute, "Hey -- this will make things easier to debug!" fixes and of course did not rerun the tests. That will teach me. Class ended with me feeling like I'd wasted a lot of truly valuable time and the students probably wondering what on earth they'd signed up for.

Transparency

So what do you do after a class like that? Well, I tried really hard to do better on Thursday. Although I did forget to have people put their names on the pre-class work, I didn't make any monumental errors. I did however, address the situation head one. This is what appeared at the beginning of Thursday's work:

First, let me start out with an apology -- we did not use your time efficiently on Tuesday, and that's a violation of the "contract" I made. I hope you all believe it certainly wasn't my intention, but that doesn't excuse it. I must, and will, do better. There are a number of ways in which things went badly, and rather than focusing on what they all were, I'd like to focus on how to avoid them. Thanks to Carl, we have a nice simple mechanism in place to help us prevent git shenanigans. Please refer to the Piazza posting. All that said, one takeaway is that at some point in the semester, if you find yourself in the midst of a git disaster (e.g., you and your partner cannot figure out how to resolve conflicts, get each other's changes in exactly the place and way you want them, etc), don't panic. There are ways out. Stay calm, learn to read git commit logs so you can figure out where things have gone astray and patiently try to fix them (we did not demonstrate the "patiently" part yesterday -- we frantically tried N fixes in a course of N-1 minutes trying to muscle through it; not a good strategy). So, as promised, today's exercise is simply to finish what we started Tuesday, ideally with significantly less drama!

I also tried to use the experience as a teaching moment, even if it was at my expense, so I also wrote:

There was another bone-headed error that got in here -- I will explain how this happened, just as a warning about "last minute changes." I had completed the problem, implemented a solution, tested it, and was happy. I then removed the synchronization to commit. "But wait!", I thought, "It's too difficult to debug, because there was no way to determine which TF is handling which student's question. The printout simply isn't helpful enough. I'll add a tf array so I can print out a TF number and that will be easier to debug." So I tossed it in the TF array at the last minute, and (here's the boneheaded part) did not rerun all my tests. So, take this as, "Don't do that!" No matter how minor the change you think you're making is, you have to rerun your tests. Especially if you're tired, that "simple" fix is undoubtedly wrong in at least three ways. Mea culpa. This was the second patch (semprob2.patch ) sent via email. Apply that patch too.

The Conclusion

So after all that, how did Thursday go? Remarkably well. The students seemed to accept my direct apology and commitment to do better. Perhaps some of them will chime in on their perspective (perhaps not; the one who are really upset will wait until the semester is over, and I understand that). And, by the end of class, all the students were animatedly and happily chatting about whale-mating. It was good to hear!

Next: Not Flipping Out (February 16, 2013)

CS161: One Woman's Adventure with a Flipped Classroom

For many years I have wanted to make my operating systems course, CS161, more interactive. I try very hard to engage students in the classroom, but let's be honest -- when they have been up all night trying to get their operating system to spawn processes, they just aren't really up to talking much in class. And when they do, it's the same set of characters and it's difficult to figure out if the rest of the class is really following along or is totally lost. At the same time, we know some typical student behavior that makes the course more difficult than it needs to be. Shockingly, even though we give students three weeks to complete assignments, they leave 99% of the work until the last week (day). That makes for a rather painful semester. Similarly, we ask them to write design documents, but many sit down to write them the night before without fully understanding what they are trying to do. And when we ask them to read the code and answer questions, they tend to gloss over most of the code and whip off quick answers.

I've always been tempted to try some newer classroom techniques, such as Peer Instruction and Flipped Classroom. I've just always been a bit afraid of balancing the potential for deriving greater benefit from class time versus dumping too much work on them.

So this year I took the plunge. I decided that I would flip the classroom for the first two to three weeks, return to a more conventional classroom while the students are deep in the most challenging programming assignments, but flip at key times, when I believe that there is real value to doing so.

I decided that I wanted to blog about this to record my observations, but also to invite students to chime in if they are so inclined. I also welcome comments from alums of the course or other others with concrete experience with related activities.

I am now one week into the semester, so we've done this for two classes. So far, I am wildly enthusiastic. It's scary, but it seems that we've already observed some tangible benefit (unfortunately, I do not have a good way to quantify/evaluate this).

Day 1

Historically I try to do a class-wide exercise where I draw the POSIX API or the programmer view at the top of a page and the reality of the hardware at the bottom and together we fill in what has to happen in between. My goal is to help students understand what the operating system must do and what they will be building over the course of the rest of the semester. As per many class exercises, a few students dominate such discussions.

So, this year I presented about 20 minutes of overview -- what the course was about, what I expected of them, what I promised in return, and then I turned them loose on three instances of the design problem (corresponding to the three main programming assignments). The TFs and I then wandered about the room, checking in, asking them questions, and helping out when necessary.

I quickly identified group(s) that were confused and were having difficult getting started. As other groups were happily making progress, and there were TFs talking with other groups, I was able to devote a significant and focused amount of time working with the groups that needed or wanted my attention. Instead of spreading attention around a class, dominated by the most confident and extroverted, I could provide focused attention where it could do the most good. Different groups addressed questions at different levels of detail, and that was OK. When I heard groups say things like, "You need page tables here," I stopped them and asked, "But what is a page table?" I wanted to force them to think through words they may have heard and make sure they really understood what had to happen.

After they worked for 30-40 minutes, I brought the class back together again and had groups present what they'd done, building upon each other, with my translating to some extent. I also assured them that we didn't expect them to complete this exercise perfectly -- after all, if they already knew how to do it, they'd have little use for the rest of the semester.

To me, it felt pretty good. The only tangible data I have is that a few students, who started off saying that they weren't really planning on taking the course because there were three other CS courses meeting at the same time, signed up. Pre-term planning number pegged the course at 37; we had about 60 students the first day; 47 registered. This is larger than the course has been in 15 years! And, it's important to realize that 15 years ago, there were no other undergraduate systems courses to speak of, so choices were significantly more limited.

Day 2

I took the material that I usually cover the first week and turned it into two videos (all the materials I'm talking about are linked from our syllabus here). For pre-class work, I had them do part of what we ask them to do for the first assignment -- get their work environment set up. Then, we spent class time letting them configure and build kernels for the first time. A few people ran into difficulty, and this was the beauty of doing it in class -- we could help them right then and there, making sure that they weren't stuck. So, within 10-15 minutes, every single student had configured and built a kernel. How great is that?

Next, we let them start answering code-reading questions (typically included as part of the first assignment as well), encouraging them to discuss the trickier ones amongst those at their table. Here is the thinking: most student spend little time actually reading the code, and when they do read it, if they are confused, there isn't much they can do except post a question (always a bit scary), email a TF, call a friend, beat their heads against the wall. However, by having them start in class, they had friends right there to work through the code with them. Some groups worked pretty independently, other groups worked completely together (two people in front of one terminal), others did a combination. Once again, the TFs and I circulated, answering questions, asking questions, encouraging discussion, etc.

They are each supposed to write up the answers to the questions to turn in, but they should have made significant progress on the assignment already.

On to week two!

Next: Flipped Again (February 7, 2013)