Lots of resources for gifted kids here:

http://cty.jhu.edu/

and specifically for your situation: http://cty.jhu.edu/gifted/dcc/underachievement.html

I did the summer programs when I was that age (a long, long time ago!). One of the most valuable things about it was being around other kids who were bored at their regular schools, or maybe also had trouble fitting in socially because they happened to enjoy and be good at learning.

If I remember correctly, the programs weren't cheap, but there are scholarships and financial aid available.