I am sorry for going off into a tangent, but what age do some PG kids level off? Does this vary also?
I'm not sure how to answer this. A PG kid will turn into a PG adult, who will still do things like understand things more quickly than most others. I would imagine that if a PG kid finds a particular passion, they will never "level off" in that field. But maybe they'll become less obviously PG to others in other areas? I don't know.
It is my understanding that "leveling off" is referring to the fact that some kids will revert to the mean, even if they picked up on some things earlier than usual. I imagine it originated from the fact that in normally developing kids, maybe all kids, there are spurts in different areas. E.g., some kids may pick up on reading faster. So, perhaps some ND kids do level off at some point around third grade, as the myth goes. But the leveling off concept doesn't seem to apply to GT kids.
