How exactly does Marion Military Institute's Academy Program work?

I'm a junior in high school, and am planning of applying at the USAFA and the USMA, and although I have some pretty nice stats, I fear that I may not be accepted with my first go at it. So I'm wondering, else than USAFAPS or USMAPS, what other military institute's are there that act as Academy Prep Schools, and how do you get into them?