I think 3rd grade at the private school sounds like the best option because it sounds like they really "get" him there. I wouldn't worry about college, yet. If he finishes high school early he can take classes at a nearby college and transfer to a university of his choosing when he is a little older.

There are other options to fill some time and build maturity such as study abroad exchange programs where he would live with a family and attend a high school in a foreign language.

I would play it by ear, just go with what looks like the best option right now. These kids change so fast it's hard to plan too far ahead.

Cathy