The parents were as bad as their girl trying to bully us into giving in to their point of view that, "it was ok", "our girl would never do that", "kids will be kids", and if "she can't take care of herself, she should find another school."
I made sure they understood that my girls have been taught to never ever start a confrontation, and to defend themselves if necessary. One day, I told them, your daughter will go too far and my girls will demonstrate that.
Not two days later my oldest was jumped, and my other daughter jumped in, and they beat the crap out of four other girls, including the bully.
I was called at work that my daughters were in the principals office and about to be expelled. When I showed at the school, the girl(the bully), the other 3 girls involved(all sporting split lips, bruises, etc), her parents, scowling and screaming at me about the two black eyes their girl had, were in the hallway. I entered the principals office where she told me the girls would be expelled.
I reminded her that our discussion earlier was about my kids defending themselves. I also told her if she made one move to expell them I would have not only have a good lawsuit, I would expose her incompetence in stopping this kind of bullying.
The other girls were expelled, my kids were vindicated and gained a little popularity for helping to get rid of the bully that terrorized a lot of them.
The behavior starts at home. Kids reflect their parents. Some of them should not be allowed to reproduce.