Question

Cherryvale appears to be some kind of prep school, or high school for gifted or well-to-do kids. Ditto for the Freemount Academy where the guys went. Since the two schools were apparently affiliated, it is likely that they would have had their respective commencements on different days. That way, the guys could park cars like they did at the parents' day event earlier in the film.

Not all of the students in the film appear to be rich. Christine Ramsey's father even looks like a working-class type, so it's possible she got a scholarship of some kind. Prep schools will do that in some cases.

Either way, they definitely seem to be very young people, hence the apprehension in getting the condoms, hotel room, etc......

God, what a great movie!

It is a private high school. We don't see the boys' graduation because it wasn't important to the story.