We chatted on twitter about this question for a bit. What predictions can you make about the predictions that were made? Click through to check your answers!


Here are the results from the 59 students who answered this question on an exam:


How would you give feedback to the students who wrote “infinity”?

Imagine that you were to give feedback to the students who wrote “-3/7.” What feedback would you give?

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I’ve never taught Calculus, and I find myself struggling with this mistake…

…in a good way. Here’s what’s want through my head:

  • Oh, God, integration.
  • How would I solve it? Is there any way that I can avoid integrating by parts? (Yeah: transform the numerator to (x-1)+1.)
  • Oh, shoot, how do you integrate by parts anyway? It’s vdu – uduvuvvvvvuuu or whaaaaa???
  • [Googles integration by parts]
  • [Solves it using integration by parts]
  • Good Lord I don’t like integrating by parts.
  • What did this kid do wrong?
  • It looks like they ended up with a square root instead of a square?
  • That makes sense. People often make association mistakes when they’re working on a problem where they have to keep in mind a bunch of moving parts.

I think that working through math mistakes like this one would be a great way to prepare for a new course.

(Hey! Someone should start collecting and organizing these so that they’re available to new teachers…)

deriv of constant


Sandra reflects:

“It’s really not an ERROR in the ANSWER, just an ERROR in thinking that they have to do any work at all to get the answer.  Perhaps an over-achiever?”

What say you all, Calculus people?

Thanks to Sandra for the submission!

I’m sitting on a bunch of Khan Academy questions from users that I marked as very interesting. I never posted them, and I feel a little cheap giving them all their own posts. So I figured I’d just dump the whole lot on you all. These questions reveal interesting things about the way these students are thinking. If you think that you’ve got something interesting to add, either on the diagnosis or prescription side of things, dig into the comments below.

The first is a nice probability puzzler. How did this student get 3/8?

I love this conceptual question.

Not sure exactly why I clipped the first question here, but the second question is great. “Why do they call it a limit?”

A good reminder: some vocab is tricky. Why are these two vocabulary words the one that this student confused?

This is a great point from a kid about variable use.

A little bit of context for this next one: we’re talking about protractors here.