<p>Since your son is now in high school, he does not have to take courses with his "grade" - he can take math at whatever level he is - the SAT 1 is not terribly high level math, so he may well need precalc and calc, etc., courses he can take in his high school. Does your school have lots of AP courses? He can take them. Languages? Is he ahead in those, too? Try to put him in courses that will challenge him, but not so that he can't enjoy his youth. Are there some classes,like English or history, where he might be able to stay with his grade (at our high school the freshman honors English all read adult books, so any age kid would be fine - maybe your son would just write more sophisticated papers.)
A combination of more advnaced courses, with some at grade level if they are not too easy, would allow him to be challenged but still have a social life.
As others have suggested, he could go to any of the top boarding schools, like Andover and Exeter, where there is a large variety of higher level courses.
If he wants to stay where he is, I'd let him. See what he wants to do. Enrichment is all around you - local college courses, summer gifted programs, etc. But maybe he also wants time to hang out with his friends or play sports - two worthy activities! Your son is very bright and I don't think you have to worry about college right now. Just do what's best for him now, and think of all the money you won't have to spend on SAT prep courses in the future.</p>