I think this is a bad idea. Even a child prodigy should stick around through Sr. Year. Kids that graduate early miss a lot, end up being very intelligent adults that are so antisocial, going to the store makes them nervous.
As for everybody else...kids are fuckin stupid as shit these days. They NEED to stay in through 12th grade and learn something. These days, you have "No Child Left Behind", so even the dumbest of the dumb fucks can get a high school diploma. I think they need to make it TOUGHER to graduate. If you don't graduate, oh fuckin' well...that's how it was when I was in school.