Of course schools aren't the only problem, but they have a huge part to play in solving the issue. Not least that for most parents, we don't see boys in groups and the way they act. I see it with DS - him alone or him and a friend leads to different behaviour to him and a group of boys. But i don't invite groups over so when I'm interacting with him or his friends, it's in a smaller, less peer-pressure driven environment.
Also, parents don't take stuff seriously enough. DD is 6. She is always complaining about children touching her hair, touching her face where she has a mole, touching her clothes.... except it's not "children". It's the boys. How or why the boys see to think this is okay, I don't know. But I deeply suspect that if I mentioned it to their mothers there's a pretty good chance I'd get some version of, "Oh, he doesn't now any better" or "Ooh, I think he likes her" or whatever. Thank goodness, the school isn't okay with this and do have conversations with the boys. But I have to wonder how far that will go.
DD also told me that she wants to wear skirts because all the girls wear skirts. But she also wants to wear shorts under because the girls get laughed at when their knickers show. Again - I have never seen this behaviour because I'm not surrounded by bunches of children playing. The school needs to help to manage this and nip it in the bud right now.