Each class has a skill associated with it. I don’t know how high it has to be, and that will increase as the terms go on. I have chosen my sim’s major and had them study those skills ahead of time. So they’re at level 6, 7, 8 -ish and acing the classes. They do most of the homework, they do their term paper/project/final exam (one of my sims was VERY late for a final and still got an A+), and they take notes in class most of the time, though I miss my chance sometimes. They don’t “study” their subjects at all. I like to match their emotion to whatever subject they are working on to gain the most from it.