Don't recall where you live, but I think it is not Minnesota. Here there is a program called "UMTYMP" (pronounced "um-tee-ump") that the most gifted math students in the state often enroll in.

http://mathcep.umn.edu/umtymp/

Obviously just specific to our state... but I suppose a few other states may have something similar. I am sure the posters out here would know!