Stray Thoughts: The best of times and the worst of times

After 30 years of teaching, I am experiencing a new problem.

In a few classes, when I assign difficult question sets, like in high school chemistry, they come back perfectly.

No wrong answers. You would think I would be pleased.

Not so. Because when I ask the students the next day about their answers, only rarely can any of them explain how they all arrived at those correct answers. Why?

Students ente…