I remember about 35 years ago when my little 8 year old girl got beat up by three 11 year old boys on her way home from school. The school would do nothing about it, so we enrolled her in martial arts classes the very next day.
Four months later, the same 3 boys wanted to beat her up again. She sent all 3 to the emergency room and was never picked on by anyone ever again.
My grandson is now enrolled in the same classes, and has already resolved his own problems with a bully.