My son, who is in kindergarten, told me he was punched in the stomach today by a classmate. Someone told the teacher, and she did nothing. Now, they preach about not bullying, but are afraid to do something... my guess, in case the parent(s) is a meth addict. I told my son that if it happens again, tell the teacher. If they do nothing, then the time it happens after that, punch the kid in the face.
You can only be pushed so far. My son will NOT grow up being a wimp. If he gets suspended, at least the kids will know he WILL fight back. And I told him I will back him up every time he has to defend himself, if the "system" won't.
Be sure you teach him to also stand up for others that are being bullied, picked on or wronged. Zero tolerance for violence promotes bullying. Bullies must always be stopped. If it takes a punch in the nose, so be it. It normally only takes one. Ignoring it won't make it go away.