I agree. I think it is definitely possible that an underchallenged PG child could show underachievement on a test. But I think most HG+ kids will be living in their heads enough that they'll advance beyond their age peers even in less than ideal situations. Short of extreme conditions, they'll still be ahead. Not as far ahead as they would be in a better educational situation, but still ahead.
DS8 took the achievement test when he was 5.5yo, and he was reading many years ahead of age level (I forget how many, but a lot). I was in GT denial, so I did not have a book available to him that was above a 2nd grade reading level. He was in K, so that should have been enough, right? He wasn't getting anything above 2nd grade in school either. But he picked it up anyway somehow.
They find ways.
