Okay, strong opinion alert:

Mia, here's what I think you should take into consideration before going into the meeting with DXH and the principal again.

You're hearing a lot of "we've got lots of/we've seen lots of kids like this before.

IMHO, I feel the administration at school is attempting to manage your expectations. I think they would say this to you even if they clearly realize there is no other child in his grade/school that appear to have his capabilities/needs.

Even if I'm wrong, I don't feel it matters how many children with higher educational needs they have. In fact, it kind of makes your case for you that they should be doing something different. Then they can accomodate your child as well as this unusually large group of brilliant children they supposedly perceive they have.

But that's not what I would say in the meeting. The bottom line is you are the parent of your own child and that is who the meeting is about. Superfluous folktales of the many other genuis children only are affective in minimizing your child's needs and I would steer them away from that line of thinking quickly.
Ex: That's great to hear the DS will have many peers here, however, I'm here to represent DS, I'm sure those other children's parents are quite capable handling their own child's academic needs. What I see is the real question is; What material is a kindergartener/first grader expected to know to graduate to the next grade. Does DS already know this/has DS already mastered this material? You can say this carefully, in a friendly manner and still not come off as overly assertive.

Your school definately has concrete parameters of what each child needs to know in order to be promoted to the next grade. If they are being vague about those parameters, I feel it is because they have already made the decision they don't want to skip for whatever reason. Try to ask specific questions and write them down so you can remember them before the meeting.
There are so many more people on this board who have better advice than I do so maybe others can pipe in.

Try to treat it as a business meeting, I know that sounds weird. There is nothing more personal than your child. But, the principle has no emotional attatchment to your or any other child, so it really is a "business" meeting to them.
Calm, state the case, friendly but not overly emotional.

Lastly, if DS is happy and doing okay, don't feel you need to borrow trouble. It's easy to read these boards and become aware of possible problems down the road. But if isn't problematic right now, know you can handle anything that comes up, as it comes up. KWIM?

So, good luck!!!!!

Incog