I thought that kids with similar high scores have quite similar achievement test results as well. It shows how little I still know or perhaps that my idea of HG+ is completely messed up thanks to DS7. Perhaps the comparison works better when the IQ is administered later on.
I think this is hard to pin as well. I have a 3rd grade son that probably wouldn't have shown his true colors achievement wise pre-kindergarten, but had overtaken some other kids that started reading at 3 by the end of that school year. And again, this kind of testing doesn't show EVERYTHING a kid knows. A kid might know a lot about geology or plumbing or star wars characters, etc and that isn't going to show up on a typical academic achievement test. My son was high with the math ability early though.
Achievement can change quite rapidly in HG-PG little ones. My DD5 is showing a similar pattern of learning as my son. A year ago, I considered her my ND kid. It's a combination of LOG, exposure, and the child's particular interest in mastery at a particular moment in time. I think over time it likely becomes a more and more accurate comparison.
I know my ideas about ND, and HG+ are just generally messed up!
