I recommend that you watch this speech that Richard Rusczyk, the founder of Art of Problem Solving, gave to parents at the 2009 Math Prize for Girls.

http://mathprize.atfoundation.org/archive/2009/rusczyk

Perhaps being at a smaller and less competitive high school would give your son more time to pursue his interests in sports and competitive mathematics. Instead of being bogged down by home/busywork in a "good" high school, he could have time to take online classes from AoPS or to study for the math and science olympiads. Moving to a bigger and better high school might also prevent him from making the varsity tennis or soccer teams.

http://mitadmissions.org/blogs/entry/applying_sideways