Last week, we discussed what to do when you make a mistake. Today, I’d like to discuss what *not* to do when you make a mistake:

I took a calculus course in college with a very good professor. My roommate took the same course with another instructor, who apparently would never admit a mistake. My roomie was looking over his class notes of a long mathematical proof or derivation, uttering “what the @#$%! is this mess!” I couldn’t make heads or tails of it either, and we had already covered the topic my class. It took us a while to realize what was going on: the instructor performed a correct but irrelevant operation in the derivation partway through the process, which led to several other incorrect steps. Apparently the instructor realized (but would not admit) his mistake, so the next several steps simply undid the previous steps! My roommate and I realized that we could simply eliminate the middle third and have a good mathematical proof.

Don’t do that to students — rather, just admit your mistake, back up (and make sure your class know that’s what’s going on), and try again.

In our next blog post, I’ll tell you about one of the best examples I’ve seen of how you *should* act when you make a mistake.