If I had a child being bullied, my blood would just boil.
No one has the right to pick on someone else. Period.
I would start where the bullying occurred and go through the entire chain of command until it was addressed.
If it didn't stop after that, I would go to the bully's parents, and get it across to them that their kid had better leave mine alone.
If they failed to take care of it, then I would go to the law and push until the kid either stopped the bullying, or got taken away and put into juvy or some place like it.
No one should have leave and run because someone else is pushing them out. After all who put them in charge anyway? Their not the boss, and if they were, then their boss needs to be notified as there are laws in place to make this stop and they need to be enforced.