An additional consideration may be that achievement tests are also a reflection of what the child has been taught. I know that they also demonstrate aptitude above level, but I can�t help but reason that if two children are equally gifted, but one is lock-stepped and one is subject accelerated, the child with more advanced instruction will test higher in that subject after a period of time.
Last year, my DS (then 10) and locked-stepped in Saxon Math through 5th grade, scored at the 97th percentile for grade level achievement and the 75th percentile against 8th grade norms for the math subtest of the Explore. According to �Developing Math Talent�, a score at the 50th percentile warrants enrichment and a score at or above the 75th percentile warrants subject acceleration. After one year of grade accelerated instruction, he took the Explore test again and earned a 98th percentile against 8th grade norms.
Both years, he scored beyond his educational experience, but I don�t think he could have improved to that degree, without some additional exposure and instruction. I guess my conclusion is that if a child scores at or above the 75th percentile on an above level test, they may very well have the aptitude to learn fast and well enough with higher level instruction to catch-up to the 90th+ percentile after one year.
For reasons that I can�t explain, I feel that math may be the most instruction/exposure dependant subject. For example, DS had scored much higher in science reasoning last year, but that subtest does seem more a measure of reasoning ability than science knowledge.
Anyway, these are just my personal opinions and conclusions.
