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02 April 2018

Targeted quiz to check for homework understanding

In the previous post, I discussed an AP Physics 1-style problem about Coulomb's law. That was my students' homework assignment due Monday.

On homework, students are allowed and encouraged to collaborate while obeying the five-foot rule. This means they may talk to one another, even look at each others' work, as long as they separate themselves whenever they're writing something to be turned in.

Yes, I do suggest you ask for obedience to the five-foot rule, even if you're at a school where copying answers is an unfortunate part of the culture.  It's difficult politically to enforce a "no copying" rule, partly because of the feigned innocence and ruthless mother-bear-defending-her-cub response you'll get by even suggesting that students might have engaged in cheating.  It's not difficult at all, though, to show that the five-foot rule has been violated, and to demand adherence: since you're not framing any requirements in terms of integrity or honesty, you tend to get compliance from students and support from parents and administrators.

Nevertheless.  I hear from teachers all the time that their students simply copy the best student's answer on homework problems, rendering meaningless the whole activity of doing homework.  Even at my current school where the students are impeccably honest and careful about the five-foot rule, I still have a minority of the class who write down a solution without thoroughly understanding it.  That's not useful to anyone. How is it possible to make students engage with the assignments?

One approach that's been successful for me is the targeted quiz.  I collect the homework... then I assign a five minute quiz asking questions similar to what was on the homework.  The idea is, students who understood the problem solving process on the homework will do well on the quiz; those who merely mimicked a friend will not do well, and thus the quiz will provide the context they need to figure out what they didn't get.

Below are the questions I asked based on Monday's Coulomb's law problem.  Take a look... see how a student who understood the homework, even with assistance from a friend, will answer quickly and confidently.  See how a student who copied a friend's answers will be clueless, especially on 1 and 3a.

That's what makes a good targeted quiz - it sends the message that answers don't matter, comprehension of solution methods does matter.  And I don't have to lecture or nag at all.  I just go over the quiz.


1. Show how to find the distance between charge 1 and charge 2 in terms of X and θ.

2. Draw and label vectors to represent the forces on object 1.

In part (c), you were asked: Using the conditions of equilibrium, write—but do not solve—two equations that could, together, be solved for θ.

3a. Explain in one sentence how we are going to get the two equations.  

3b. If we are writing two equations, how many unknowns may there be in the equations?

3c. What is incomplete about these two equations as the solution:  

Tcosθ  = mg
Tsinθ  = Fe

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