A not very well-known film which I find morbidly fascinating, called "If...", from the 1960s. It was in a boys' boarding school, was extremely radical and daring at the time, and some moments in it were absolutely brutal. I watched it at the age of 15, and I loved it then, but I can't imagine one being made like that now.
Some scenes were:
A fat boy being teased while undressing; I would quote some lines, but they might be triggering. (Seriously!) Also a boy with his head put down the toilet.
All the boys showering together, while being bossed about by a prefect (a "whip") sitting in a bath, who was waited on hand and foot by a younger pupil (a "scum"), and who made boys he didn't like have cold showers. Although no genitals were visible, it's rumoured that some shots of them were later removed.
The matron giving the boys their medical check, shining a torch between their legs, in front of the whole school (although the boy would have his back to the school).
Two truanting boys stealing a motorbike, then trying to seduce a café waitress; she slaps his face when he tries to kiss her, but later they're seen rolling naked on the floor.
Three sixth form boys being brutally caned by a prefect, for "being a danger to the morale of the whole house". This scene was legendary among lovers of this film.
And finally the ending, which was so controversial, and loved by those who hated school, the filmmakers sent a fake script omitting this scene to the school where it was filmed. (I can't post it here - spoiler alert!) 