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24 July 2017

Ask for an answer LAST

Greetings from the American Association of Physics Teachers meeting in Cincinnati.  The exhibit hall opened last night with self-serve all-you-can-eat Skyline chili.  I have ascended to my eternal reward.

Since I arrived, I've done a wee bit more than eat chili and tour Great American Ballpark.  Yesterday I attended the High School Teacher Camp, organized by Kelly O'Shea and Martha Lietz.  We spent the day talking shop, meeting colleagues from around the country.  The keynote address was from Kathy Harper, discussing student perceptions of "mistakes" in physics class and how to channel those perceptions in a positive direction.

I've got a *lot* of notes on my phone which will inspire future posts.  For now, I'm going to relay an idea from Martha about her revised approach to AP Physics 1 justification problems.

I've written before about issues teaching students to articulate their reasoning on semi-quantitative or conceptual questions.  In sum: English class, history class, geometry class, and Fox News have taught students to begin arguments by picking a conclusion; then, to construct quasi-logical arguments twisting evidence to support that result, truth be danged.  Students are not used to the idea of beginning with the logical evidence, and then dispassionately asking what conclusion should be drawn from that evidence.

Of course, getting students even to articulate a quasi-logical chain of evidence is a tough challenge in physics class.  Come on, teacher, you know the answer, (think I) know the answer, if I'm right why do I need to say any more?  To break this first barrier, Martha had been an advocate of the "Claim-Evidence-Reasoning" approach to justifications.  For each problem, she would give space for the student's claim, i.e. their answer; for the student to write evidence from the problem statement or experiment; and then for the student to link the evidence to the claim through verbal and mathematical reasoning.  She required every student to address every element on every problem set.  

And it worked, sort of - Martha's students were willing to articulate their reasoning using words and equations.  Great.

But it was obvious to Martha that many students were merely guessing at the right answer, then cherry-picking evidence and reasoning that could support that original guess.  I've seen this intellectual stubbornness as well.  I don't know why people's brains have so much trouble adapting knowledge to new evidence.  I just know that they do.  Once a student decides that the answer is choice C, it takes an actual invasion by the Red Army to convince him that maybe the evidence points to choice D instead.

So, Martha suggested... why not ask for an answer LAST?

She subverted the paradigm to Evidence-Reasoning-Conclusion.  After the problem statement comes space for students to write evidence: facts, equations, and information relevant to the situation.  Then comes space for the reasoning: use logical connections to explain where the evidence points.  And finally, at the end, the conclusion: that is, the answer.  

Because the answer comes last, because students are not asked to commit to a conclusion before examining the evidence, students actually, well, examine the evidence.  They stop contorting their logic into pretzels to prove themselves right, and they start doing physics like a physicist.  Martha no longer has to suggest that their answers might be more likely to be correct if they'd use physics.

How am I using this?  I intend to rewrite some of my problem sets, especially in conceptual physics, making just one small change.  Problems have previously looked like this:

[Problem statement blah blah blah]



But I'm going to take a cue from Martha, and rewrite this way:

[Problem statement blah blah blah]



Let me know what thoughts you have, including whether this approach does or doesn't work for you.


  1. It's crazy how such a small change makes a big difference. I think once they're used to the process and we're in review mode, we can work on AP problems that aren't formatted this way since that's how they'll be on the AP exam. We'll have to practice ignoring the answer choices until we've finished working through the justification. Any idea how to convince students to do that?

  2. Nadia, I think you already convinced them! "Once they're used to the process and we're in review mode..." If you've worked through evidence-reasoning-conclusion all year on AP-style problems, then I don't think they'll have any issues adapting to the format of the actual AP exam. You'll have ingrained the correct reasoning process so that format doesn't matter anymore.