I do not know if there is anything to this, but I'd read that:
"For girls, in particular, early IQ scores are more reliable than those obtained after they have been socialized into hiding their abilities.
At the Gifted Development Center, we have found that the optimal time to test gifted children is between the ages of four and nine. We find that at the age of nine, test scores for gifted children usually decline, sometimes as much as 20 points, due to (1) ceiling effects (test items not being sufficiently difficult to measure the full range of abilities); (2) perfectionism (particularly in girls), leading to unwillingness to guess when uncertain; and (3) the increased emphasis on crystallized (learned) knowledge and skills rather than fluid abilities (purer forms of abstract reasoning, considered innate)."
http://www.malonefamilyfoundation.org/whatisgifted_assessing2.html
