> Boarding schools have always been for a minority
I sincerely doubt this. I’m not sure if my father’s school had day students when he attended but boarders were definitely a large majority. The omnipresence of boarding schools in post WWII British fiction doesn’t make any sense unless there was at least rough parity among independent schools. CS Lewis, George Orwell, Roald Dahl, off the top of my head. Seamus Heaney after looking it up.