There was a strict school boy code about fairness strongly enforced by the boys. I know nothing about what the girls got up to. The code prohibited picking on those smaller or weaker than yourself. You could not be sneaky, or attack from behind, hit anyone wearing glasses, no kicking, no weapons of any kind, etc. Nor would you allow anyone to get into trouble for something they did not do. The culprit would own up. No one informed on others. The teachers supported the code and they certainly did not like tell tales.
Codes such as that described are very much better at protecting the vulnerable that anything teachers can do. The establishment and continuance of such codes is supported if children are taught about duties and responsibilities and not just their rights. Of course, adults must set a good example.
Much of the bullying that went on in our school , was undertaken by staff against pupils.