re: 1 school in USA

ALL players improve from High School to college, and then from college to Pros. Combination of their bodies maturing, their minds maturing, more intensive practice and coaching time. In high school a coach gets 2-4 hours of practice time a day. In college it's 3-5. In the pros it's more like 7-8. In high school it is limited by class time and parents. In college it is class time and study time. In the pros they get paid, so they are expected to work out, study sessions and on field practice.

If a player does not play better from one level to the next, he won't be playing at the higher level much longer.

I keep seeing where people complain that the coaching staff does not do their jobs because players flourish in the pros. Ask a pro if he feels he is playing at a much higher level than he did in college and see what he says. Then ask him why.