but I believe most prep schools offer scholarships to players.
Those scholarships are funded by an endowment that anyone can help fund, and preference "might" be given to certain players for scholarships based on who contributes to the endowment.
At least that's what I've heard, and if it's truly the case, it's a very unique way for prep schools to basically allow boosters to pay for a guy to go to prep school while skirting the NCAA rules.
Anyway, on your question, I believe prep school vs. Juco is determined by graduation. Someone correct me if I'm wrong on that, but I don't believe you can attend prep school if you actually graduated high school. If you came up short of graduation, you can attend prep school to finish your high school education. Again, I could be wrong on that, but I heard that somewhere.