Most of the teachers are in the teaching business because they would like to bully adults but they're too weak to get away with it, so they settle for children. Causing pain is the point.
You're not allowed to call the teachers bullies though, because you might well get arrested if you do it sincerely enough. Therefore they're not bullies, right? Right.
Because the teachers are torturing the kids for sadistic kicks, the kids get stressed. They can't take the stress out on the source, because of the aforementioned armed police escort. Therefore they take it out on other kids.
There may be some marginal crazy person / psychopath native bullying, but almost all of it directly traces back to the teachers.