The way I see it is that a teacher may help a pupil to understand something by identifying the pupil's misconceptions. These are unique to the pupil and the tea

The way I see it is that a teacher may help a pupil to understand something by identifying the pupil's misconceptions. These are unique to the pupil and the teaching process includes to-and-fro questioning aimed at identifying and blasting them away. (Teaching a group of N pupils is hit and miss, since a teacher can't go in N different directions at once. Instead he explains something in different ways until the common misconceptions have been covered. He doesn't know what these are until he has taught many classes on the topic.)