When my daughter was in 4th grade she had some little boy that would pick on her. I didn't go to the school, I didn't threaten the kids or his parents, I taught my daughter how to fight!
Put her in a taekwondo class followed up with boxing lessons. When she went back she said the boy was still messing with her. I told her it was OK to defend herself. The next day I got a call from the principal. My daughter had broken the little boy nose.