When good students turn in an essay, they dream of their instructor returning it to them in exactly the same condition, save for a single word added in the margin of the final page: Flawless.

The author looks upon his mother as his most demanding and caring instructor.

I've only had two driving lessons so far, and my instructor is very understanding.

Twenty pounds an hour, and the instructor says I'll need about30 to 40 lessons in total.

Meanwhile, a second group was directed to solve the same problems by collaborating with one another, without any prompts from their instructor.