I think the idea is that the teacher want to make sure that the students understand the lectures she's about to impart and that they understand the chapter they're about to read.
I recall my first day ever teaching at college. I was terrified, but had muddled my way through it. I was explaining then for about 20 minutes or so how to go about conducting their first lab. I said, "When the cursor is here, you do this. When the cursor is there you do that." After 20 minutes, somebody timidly raises his hand and asks, "What's a cursor?" It had never occurred to me that someone would not know what one was.
And it's not like the definitions are fixed in one's mind. Most definitions in a history class are going to be necessarily vague. Over the course of the studies, what the terms actually mean become solidified in the students' minds.
Many teachers in this school are very big on giving outside reading. In AP Bio, for example, the teacher has already given a number of articles on protein-folding, etc., to the students - material which they are quizzed over in the following class (before discussing). They have two quizzes a day, almost every day in that class. Five simple questions at the start and end of every class (no idea when the woman finds time to grade this stuff).
At first she (my brat) complained that the articles didn't have anything to do with the sections they were working on, but then later, she it really was, but it wasn't obvious at first.