I think schools are here are some reasons
#1 they will always say you can do better then that making you think your not good enough
#2 there are other students who are doing better then you making you feel pressured to be as good as them
#3 they give you a lot of homework meaning you will sometimes be sleep deprived leading you to be unhappy or depressed
#4 some people will have more friends then you meaning you will feel like there's nobody to talk to about your emotions there for keeping them bottled up
#5 you will always think people are looking at you causing anxiety
I say these knowing there real from past experiences and that's why I think school is the root of depression