On the side, I sometimes tutor high school students, usually in chemistry, but have done most subjects. I usually get a call a day or two before a test and the student needs to review the whole unit, so it turns into a marathon session.
It is amazing to watch the moment when the student shuts down from overload. They are unable to figure out each next step of a problem without coaching, even on problems they know how to solve. They make dumb mistakes. Their eyes are glazed. When you hit this point, it is time to stop, mid-problem even, tell them to go to bed, get rested and tackle that problem from scratch in the morning.
