I went to a small high school in central Texas. My graduating class was 102 people; it was supposed to be 105.
A dude killed himself in our junior year: ran away from school and jumped off a nearby cliff - we were situated high on top of a hill, surrounded by near unpassable bush leading down to a river. It took the detectives several months to find his remains, and they only recognized him by his Hawaiian shirt.
Another kid that was supposed to be in our class but got kicked out for potentially being a liability due to psychiatric issues really did become a liability several months later.
Then a friend of mine killed himself our senior year - hung himself on the eve of the Theology final. He always did have an odd sense of humor. By that point the newspapers started picking up on this weirdness and running speculative articles about our bloody lemming class.
Our last self-inflicted casualty happened last February: a really brilliant Hopi kid from the 2000 class descended into alcoholism in Los Angeles and killed himself. He was heavily involved in outdoors activities when he was in high school, and most of the outdoors club was from the 2001 class, so far more people from our class showed up for his funeral than from his. By-word at the funeral was, predictably, "We've got
to stop meeting like this." It's kind of sad when the only reasons your class gets together is to bury a peer.
As to why they did it... I can't generalize, obviously, but there's probably a reason why some parents send their kids away to a school deep in the hills where no one is allowed on or off campus without permission. Academics and sports aside, it's a great excuse not to deal with your offspring if they start being a handful. Not that we were considered a school slash prison for young psychos and criminals, just the opposite - the understanding was that everything was super-fluffy and safe and friendly. People left their stuff everywhere without being afraid of theft, and a single fight was grounds for expulsion. A very expensive boarding school for the very rich and whatever poor kids they select to add to the "diversity" bouquet. But if you have to live with the constant thought that you're here because you're too much trouble for your folks to handle, then that probably doesn't help. It's not like every parent dotingly called every night and came to visit and have lunch with you on weekends.