Is there any laws against overreaction in school punishment?

I would imagine that drawing a swastika would be taken as highly offencive and potentially racist. You can appeal any decision to expel you, and if this is your first offence of this sort, it would be fair to argue that they are over-reacting, but the best way to get around this would be to apologise, and learn that this sort of behaviour is not acceptable to the vast majority of people, rather than treat it like a bit of a joke.