Hi 22B! Your DS sounds a lot like mine, now 9. We have no formal test results for him (it's a lot less usual here in the UK, and there's never been a positive reason to do it) but he was also an early self-taught reader, late talker, bad sleeper, and very mathy (does well in comparisons with mathy people twice his age, both in problem-solving and in syllabus, even though we've been trying hard not to have him speed through syllabus, preferring to get him to think). Also, very good memory, can be slow. Writing was a particular problem until recently, but with some good help from school (and switching to fountain pen) he's doing amazingly much better now.
Not sure whether I can actually be any use, though! We're very fortunate in DS's school; he's with agemates, but in small classes (15) and, I think, enough differentiation that we're likely to leave him with agemates. (He may, or may not, collect one year of acceleration when we move him to senior school at 12/13 - depends where he goes.) I have strong opinions on how to nurture mathematicians, but it may be that you do too ;-) In brief: mathematics is about solving hard problems, not about being able to carry out algorithms; so acceleration to work with typical school material but with older children may be a useful ingredient, but it's definitely not a complete solution.
