Even with a FSIQ at the 99th percentile, he is more than moderately gifted. Unless your community is a planned community of Intertel members or something, I can't imagine that those scores aren't that special in your area. A district of high achieving professional families will likely have more gifted kids than avg, but I'd be willing to bet that a lot of their kids fall around the 95th-98th percentile, not above.
With the achievement scores, I'd say that you have good data to support your request. Like others have mentioned, write up your notes first so you stay focused! What was his PRI score on the WISC? That's the part that most schools look at when identifying kids as gifted in math. If that was high, that might provide you further ammo. Good luck!
