Welcome whattodo. I'm sorry that you're having such a hard time. I'm not in Florida, so I can't help there.
But your story sounds very familiar. We had our DS in the local kindy when he was 5, and they gave him 2nd grade math, and then we advocated for a skip. After much work, we got the skip into 2nd, and with much more advocacy, we finally got things a little better, thanks to the school staff and GC being flexible. We are in a small district, so they didn't have a lot of experience with HG kids, which I think helped as we were able to suggest things. Is there any chance that the school would allow your DS to work on online math such as Aleks or EPGY while the other kids are doing grade level math? Are there any other schools near you, not necessarily identified as GT schools, that might be more flexible? A lot of GT schools just work a year ahead, and that's that, and they're not too flexible. Smaller schools with less experience with GT kids but with more flexibility might be a better option, if available.
We did end up transferring DS mid-year to a school for HG kids, which does work a year ahead, but faster too. And they group kids by ability as well, and it's been great so far. So if you find a school that will skip your kiddo to 2nd, which it sounds like he needs, then maybe a mid-year transfer to a GT school is also an option, though obviously not an ideal one. Just throwing that out there.
The one thing that has been harder for our DS7 is writing, both handwriting and mechanics. He is way behind the kids at his current school, and it's been kind of tough for him since he notices he's way behind. I highly recommend working on writing over the summer if a skip is a possibility (if writing is an issue for your DS).
Oh, and the best advice is to stay friendly with the GC. We had a few run-ins before our transfer where we got really upset, and that didn't help anything. Try to remember that the staff at the school really does care about your kid and do want him to learn, but the reality is there are 20+ other kids too. I would suggest getting your hands on the Iowa Acceleration Scale and filling it out with the school. That finally convinced our local school that a skip was a great idea for our kid.