How come my sims keep failing university classes

A lot has already been said, but one other aspect (and I could be wrong) is I think your sims skill level in the "subject" might also have an impact. Like, I've had sims who seem to do "everything right" (attend class on time and in a good mood, submit excellent papers, do all their homework, yadda yadda) and still not get great grades (tho I've never had a sim actually FAIL a class), and then other sims making pretty minimal effort (hardly ever doing homework, being late or even missing a class or 2, one sim straight up slept through her final lol) and still get an A or A+, and the difference seems to be that the latter group, despite their class participation, still HAD very high skill levels in the classes they were taking (like, 8, 9, 10 levels I mean) while the first group, despite all their class work, were still fairly low (usually around level 4 or 5). So, it might be the case that if a sim is just "good" at something, they can kinda breeze by, while a another sim who is fairly low level has to put a LOT more effort in.