Everything.
Science is all made up by man, some of it's proven correct, some not.
Math seems to work, but it gets pretty insane once you hit Algebra 2 and up.
History is fucked. Everything untill recently was just the word of whoever wrote the shit down, and even now with all of our technology, sometimes because of it, our History classes are bullshit. Social Studies falls into the History camp.
English/Literature classes can be good, but usually they're taught by some writer who couldn't make it, and now they're bitter, and makes they're classes hell for their students.
They lie to you in every class in every school, because each teacher does one of two things.
1.) They go by the Teacher's Manual, those things are horrible.
2.) They teach shit their own way, totally fucking you in any other class for that subject because that class will be taught by a teacher that goes by the Teacher's Manual.