There may be many solutions, but I think the number one protector of a child SHOULD be the parent.
Perhaps in some cases, the parent is not aware, through no fault of their own.
But if they are aware, I believe it is their responsibility to see to it that their child is in a safe environment. Whether that means confronting the other parents, going to the principal, switching schools, home schooling, turning off the cell phone/Facebook, whatever.
Also children should be allowed to defend themselves just like adults are.
Continuing along the line of parental responsibility, the parents of the bullies, once made aware of their kids’ behavior, should be responsible to put a stop to it. Or have to pull their kid out of school. Or be held criminally liable for their bully’s behavior. Just like a parent is responsible for their child’s stealing or vandalism, or should be.
Adults are not allowed to defend themselves in areas run by liberals.