You learn to shut up and listen to a nasty ignorant authority figure drone on about something they are quite wrong about.
You learn to do what you're told, even when it's humiliating or boring, because standing up for righteousness just gets you in trouble.
You learn how to comply with some horrible dumb rating system that grades you on what a clever diaroma you made. Don't try to do what's actually right, do what the rater wants. (something that Top Chef contestants seem to constantly fail at)
You learn to just suck it up and plug through some drudgery. Work that's pointless and boring and will just be thrown out when it's done, but you've been told to do it, so you do it.
Obviously you learn a lot of social lessons as well, like don't stand out (except in the group's accepted ways of standing out) but today I'm only talking about the academic lessons.
I don't mean that it's bad that school teaches you these things. They are important lessons, and you will need them in your career if you want to be a successful conformist worker bee.