I've lived with this kid for his whole life and in looking at the various "levels" charts that are out there, I've never considered his behaviors to be at the upper-end... or any where near the "scary" gifted, which is what my sibling is. I've lived that life with him for years and just don't see it here.
your sibling? Ahhhhhh I've often read that gifted parents don't see it in their children b/c their children seem more normal/average to them.
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As for the school -- I'm hearing whispers suggesting the opposite: "We've not had a kid like him before and don't think there's anything we can do within the school."
There is a homeschool boy which I've been told is so far out there to be unmeasureable. I've seen this kid in a book discussion group and I know he'd be just fine in a college level discussion and he's 9yrs old lol. He takes all his courses through CTY online (math, science, language arts). That may be an option for your son if he likes that sort of thing and still do art, music, pe with his classmates at school.