## The role of the teacher in peer instruction

The radical constructivists tell us that a teacher who tells the students anything “steals from them the opportunity from them to learn it for themselves.”  The role of the teacher is to be a guide and facilitator.  My first PhD advisor, Pat Baggett, used to say in response, “Not all students are Newtons.”  (Computer scientists may not realize that these debates really do go on in Education schools — Pat literally said that line, several times, in several different settings where I was present.)  Few students can construct complex ideas like Calculus from experience and first principles. The point that inference is often hard for students came to me again this week.

I continue to teach my data structures class using peer instruction.  We’ve been working our way through recursive traversals of linked lists and trees this week, with trees containing sounds.  We had just talked about the method for collecting all the sounds from a linked list of sounds, declared public Sound collect(), when I put up this slide.

In discussion about the code, it was pretty clear to me that they were confused what collect() was really doing, so, on-the-fly, I drew up this slide.  In a linked list with three notes in it (middle C C4, E4, and G4), how many sound objects will collect() return?

Let’s consider the pieces of data that the students have.  They’ve seen the code public Sound collect().  They can see that collect() is asked to play(), and only the class Sound knows how to play. And there is the fact (perhaps not inferred yet by the students) that Java methods can only return a single object — even when it’s an array, it’s just one object.

Here were the responses:

Lots of students see 3 objects coming back from collect().  I let them argue it out, while I wandered the room — responding to questions, listening to how the arguments were being made.

Second vote time:

More students are coming to see that it’s only one object coming back from collect() (which appends all sounds together, simply digital splicing).  But still many think it’s three objects (and are confident — nobody’s choosing “IDK” for “I Don’t Know.”) We then had a great discussion, where students insisted that there were three objects being returned, and I addressed their arguments (e.g., if you add three raindrops together, you get one big raindrop.)

I’m not arguing that my students are dumb.  Through peer instruction, I have come to understand better what they understood coming in, how well they understand what I’ve been teaching them, and how far they’ve come.  They’re really learning alot.  But they’re not learning it alone, nor even just through social learning and peer interaction.  The teacher is needed, because students can cling to wrong ideas and can avoid inference for a long time.

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• 1. Paul  |  March 16, 2011 at 2:15 pm

Is there a specific paper on peer instruction that you recommend for someone who’s interested in understanding the theory behind it and the process if incorporating it into a CS class?

• […] in a large class.  This is a cool piece, and I buy it — that’s why I’m doing peer-interaction in my class.  I still believe that lecture can work, the evidence is strong that […]

• […] A lot of my work these days is about pedagogy.  I use peer instruction in my classrooms, and try out worked examples in various ways.  In our research, we use subgoal labels to improve […]

• 5. Mike Lutz  |  December 21, 2012 at 10:25 am

I like peer instruction as well, but perhaps it’s my inflated ego that says I know things they don’t know, and they’ll never know (or take eons to know) if they just flail about with equally ignorant peers. (Note I said ignorant, not stupid.) To build on the physics example (from Newton), it’s all too easy for a group of students to conclude that heavy things fall faster than lighter ones, or that the astronauts didn’t float off the moon because of “heavy boots.”

• 6. Mark Guzdial  |  December 21, 2012 at 10:29 am

Absolutely agreed, Mike. So the trick is to prevent flailing about. Beth Simon has been working hard at figuring out the right kinds of PI questions — those that encourage productive discussion, and discourage wandering around lost. What we know from cognitive science is that students learn from what they do and think, not from what we tell them. Listening to more of us telling them the truth won’t lead to as much learning as them realizing that what we said earlier was actually right.

• 7. Mike Lutz  |  December 21, 2012 at 10:46 am

As a followup: There is a world of difference between knowing something, comprehending it, and being able to apply that knowledge (to borrow from Bloom’s taxonomy).

There is little chance that students will develop the limit definition of the derivative on their own; this was an inspired insight by Newton and/or Leibniz. IMHO, this must be taught more or less directly, but with liberal use of graphs, etc., to appeal to student’s intuition.

Comprehending this definition – really grokking it, to use a Heinlein phrase – will require practice for most students via use of limits to find lots of derivatives – primarily polynomials at first. This is probably a place for closely mentored peer activities.

The final step – applying this knowledge in new contexts – would seem ideal for the “guide on the side” approach, assuming you can convince students to call for help when they need it. A lot of the success here depends on the teacher’s ability to establish a non-threatening environment where questions are valued, not ridiculed.

And, of course, we must be humble enough to recognize that some students will NEVER get it, no matter what WE do. They aren’t stupid (unless science and math are the sole indicators of intelligence, an abhorrent idea to me), their minds are simply wired differently. We all have such weak spots, if we’re honest about it, and we should commit ourselves to helping such students find the area where they’ll shine. And it may not be at college.

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