Here is a simple way to stop a kid from bullying your child: File a civil suit against the Parents of the bully(s) File the case under "harassment" and seek monetary damages.The American answer for everything: sue, sue, sue.
Reading these situations...if they were to take place in the adult workforce - it would called SEXUAL HARASSEMENT.The female answer for everything: the sexual harassment trump card. If you don't like something someone does or says, scream harassment. That will usually get them in hot water or fired, and you don't need to prove anything.
One of the most important things a bullied kid needs to realize is that the way the person treats you shows you what kind of a person he/she is, not what kind of a person you are.This is akin to saying "sticks and stones," and that is really no help when you are getting the tar beaten out of you.
When I was a kid, I was picked on a lot. With an IQ of 144, I was in the 99.83th percentile. When I was in the 7th grade, I was tested on math and reading skills and maxed out the test: College Junior. It may have been higher, but the test scale went no higher, so there was no way to tell.
I was picked on and called geek, nerd, etc. Even the teachers sometimes participated. The abuse would sometimes get physical. It was so bad that I would not let my children be placed in a so-called gifted program when they were in school. When the abuse turned physical, there was one thing that stopped it EVERY TIME: I learned to fight back. When the abuse turned physical, I punched the bully in the face. To my parent's credit, they went to school and defended me against the "zero tolerance" rules that the school had against fighting.
I did the same for my kids. When my son was in the second grade, he came home crying because a fifth grader was beating him up on the recess yard. I went to the school and was told that the teachers can't be everywhere, and that they couldn't discipline the bully unless they saw it happen. My son, who was playing Pop Warner football at the time, was told that the kids on the football team were larger and hit harder than this bully did, and the next time it happened, he should fight back.
He told me that the teachers were teaching them that fighting was wrong, and that the policy was that both students were to be disciplined if a fight broke out. I told him that I would take care of the teachers, and that he should never start a fight, but if a person attacks you, you should defend yourself.
Several days later, I was called to the school because my child had beaten the bully pretty badly. The kid went crying to the school office. When I got there, I saw that the child was twice the size of mine. The school wanted to suspend my son. When I asked them if a teacher had seen the fight, they replied that no teacher had actually seen it. I then pointed out to them that they told me that if no one had seen the event, they couldn't do anything.
"After all," I said, "teachers can't be everywhere." (is that like the saying that the police can't be everywhere?) I then told them that I would never raise my child to be a dysfunctional adult that knuckles under every time someone attacked them, and I certainly would not teach my child to stand there while someone beat the tar out of them.
The bully never touched my son again. In the same vein, that is why my son received a .45 caliber handgun from his Dad for his 21st birthday. He has a concealed weapons permit, and carries that pistol frequently. The schoolyard bullies of yesterday are the violent criminals of today.
Well, sometimes they get jobs as cops, but that is a story for another day...
Edited to add: All of this "don't fight back" nonsense forces kids to bottle up their hostility and resentment at being picked on until they snap. I believe these policies are the reason why good kids who are bullied go on shooting sprees. See Columbine. Reminds me of the Pearl Jam song Jeremy.