This is actually a good question that people may not read into very well, and the OP probably knows but didn't indicate: Humans have a circidian rhthym which is a component that indicates when you naturally want to wake up and sleep. Thoughout our lives it changes at different points, but the important point is that for teenagers, they want to be up at night and also wake up later(almost the exact opposite of elderly people).

So trying to make students sleep at 10pm is very difficult vs having school start later to allow classes to better match their sleep cycle.