this is and has been a part of the school experience since schools have existed - but that doesn't make it right.
it's a tough issue. tough for the victims to report it, tough for teacher's to see what is really happening - and tough for parents to trust the schools.
but if it's on school property, this is something teachers need to be empowered to handle.
They should be allowed to suspend trouble makers from their classrooms, and if necessary, from school. Student's coming near school property while suspended should be arrested and brought home.
THEN it's the parents' issue. And they should be civilly liable for bullying behaviour after that point.