Basically, they put you through hell, both institutionally and Lord Of The Flies. Bullying was normal, and vicious, and inescapable (no going home to get away from them). You dealt with it or you persuades your parents to let you leave, or you suicided. In my school of ~400 pupils we had at least one suicide a year, often more.
The thinking was that if you survived all this then you would be sufficiently tough (mentally and physically) to be sent to some colonial outpost far away from everyone and everything that you knew, with no help nearby, and not lose your shit.
It kinda worked as intended for most people - ex-classmates I've met since are confident and charming. But for those like me, who didn't get on with the system so well, it was years of clinical depression and therapy to heal from it.
There's a name for it now: Boarding School Syndrome [0]. It manifests in adulthood as a range of symptoms, but emotional detachment is probably the most prominent. It's not healthy, and realising that almost all of Britain's most prominent politicians suffer from it (and every single British prime minister since Thatcher went to boarding school), it becomes obvious why Britain is such a mess now.
[0] https://caldaclinic.com/boarding-school-syndrome-the-childho...