It is hard to stereotype the kids, they are all so different.
I agree about this early reading that many times seems to level off. The family I know of had their oldest child accelerated from K to 1st. Then in second grade the Cogat testing didn't even show that it was high enough to put the child in the enrichment pull out but yet they had been grade skipped the year before????
I am particuarly sensitive to this issue because we had tried to have my HG son accelerated and his IQ score was fine. His achievement tests (especially writing) were low so this same school wouldn't move him ahead.... We just spent more time in preschool years following his interests rahter than "prep'ing" him for school before it even started.
Thankfully, we are in a FT GT school now and it doesn't matter.
What's frustrating is our orginal school seems to value early achievement (even though it was so parent led)more than anything. Had my son stayed in that school and tuned out because of boredom at the slow pace they probably would have never realized what he was capable of.