I think JBDad's point that they're all different--so even though your child doesn't do that particular thing that some other astonishing child does doesn't mean they're not HG+--is a vital one.
What's your child's "thing" is going to be different from the "thing" of some other HG+ child. You can't really compare apples to oranges. I like to point out that milestones can help a parent to recognize GTness, but I don't think that their *not* reaching early milestones should be used to rule out GTness. There are too many complicating factors there.
It can be reassuring to those of us in GT denial to say, "Oh, well, my child can't do THAT, so we can mange easily" though, can't it?
