Wasn't there something about gifted students not necessarily translating into gifted adults? And that it's just that they are faster to reach a level of development, but doesn't mean they will go beyond the normal limit.

Like the rate of development and learning just follows a different curve, but ends up near the same point once an adult.

I think it was only some gifted student retain an advantage in adulthood, and it is normally when they are gifted in a specific discipline for which they maintain a consistent and continued practice through to their adulthood.

That's kind of what we would expect to happen in the case where other kids get actual support & "gifted" kids are left to fend for themselves, or even sent to the library to keep them from disrupting everyone else.

You can just as easily measure the second derivative, i.e. see how fast they are improving at improving.