To expand on what Jack'smom said-- a 504 does not provide services, only accommodations. (A 504 is binding, but it is for "equal access," things like wheelchair accessibility and extra time on tests to even the playing field.) If you want actual services to remediate the disability, you need an IEP.
It is false that they are not obligated until he's been in school two years-- in fact, they've had obligations to him since he turned 3. You need to write a letter to the person who is in charge of services to the disabled in your district, copied to the principal, and ask for a full evaluation-- tell them everything you suspect is difficult for your DS. Be thorough, because this request determines what testing they do. There is a template in the book From Emotions to Advocacy. They then have 60 school days to get their evaluation done. Be prepared to bring your outside experts and their written reports to the meeting that results from this process, so they can detail in front of the school personnel what work has been done to get him up to grade level and what's needed to keep him there.
I don't know that I'd personally bother much about the GT services (how good are they for kindergarten?) at this phase. Once you remediate the disability further his true colors may show more clearly. In our district it's impossible to get someone into GT without the right scores, even if a disability is lowering those scores artificially. I'd say learn more and get the disability stuff firmly into place before you decide whether to mount a charge on the GT.
DeeDee
