I don't agree with that. Some kids entering K have been taught, worked with, others don't know the alphabet. There is not necessarily a correlation with their innate ability.
I'm not saying they all even out, but it is true that by third grade as compared to K they have all had exposure, and instruction, and any effects of early interest or instruction will be gone.
BUT. The OP's kid has a gifted-level IQ score. Surely that counts for quite a lot. If her child was simply an untested high achiever, that would be different.
