You mean like circle jerks and stuff?
Someone mentioned public schools being heavily represented by senior military officers.
Not for everyone I'm sure but the vast majority of cadet groups are in private schools despite being MOD funded. Get into it and the encouragement is to head for Sandhurst.
You get opportunities to try out and be good at virtually anything.
State schools don't have the money to offer a vast range of activities and experiences.
Upper end private schools can be over 30k for a boarding student per year and that's how they do it.