It's a thing they still do. My old school stopped boarding in 2014, but they still have a cadet force. Lots of private schools have Combined Cadet Forces, or CCFs, which offer Army, RAF and Royal Navy cadet training. I was in the air cadets for 5 years, we went shooting most weeks, camping most summers, flying about once a month. Our school armory had mostly L98A2 "Cadet" version of the SA80, but we also had some SMLE No.4s adapted to fire .22, and occasionally we'd go to the range to fire the SA80 LSW on fully auto.