There are people far more knowledgeable on this board than I. That said: Welcome.
We had a similar situation with our DS5.5. We were scheduled to enter K this year. During the summer we got DS formally evaluated, an expensive but a necessary step. Even though our state will test children, they operate on their own schedule. We wanted an independent opinion. Something more than "we (parents) think he's bright". It's unfortunate, but when you look at it from the SD's perspective they get lots of requests for special exceptions from parents. Having hard data helps make your case.
After getting the evaluation where it showed that his mental age was above the requirement for early admission into first, we submitted a formal request. This, though, was specific to our local SD's policies and procedures.
What you might want to do is to start learning about your local SD's policy. Sometimes grade skips can be difficult to advocate for. But as someone once told me on this board, there is always someone higher to talk to. Principal, Assistant Super, Super, Board of Directors, etc. If there were no barriers, what would you want for your DS? Skip into 2nd? That would seem reasonable to me.
My two cents. Let me know if I have change left...
JB
