Doesn't that sound like my second paragraph?

But there is an assumption here, that childhood IQ predicts adult IQ. In fact, it isn't very good at age 8. The SMPY age of 12 is better, though by no means perfect. When I say "good" or "better" I mean, of course, stability at the center, which might not predict stability at the tails. When SMPY finds that age 12 tests predict life outcomes, they are testing this directly. But what we really want to know is whether the SAT score at age 12 adds information to the low ceiling SAT score at age 17. I think that the SMPY results are strong enough to guarantee that, but I haven't checked.