...Our school probably has 30% of the population that has been identified as gifted but not all are in GT classrooms...
Our schools place all children with GT identifications into GT classes and, like yours, once you are identified you are in those classes throught 12th grade unless your parents agree to have you in a non-GT class.
I believe that CoGat does over-identify especially at the lower grades...
I think that this is particularly true for kids that move into the program in the later grades. For the older kids, I think the move seems to be based on a less than ideal experiences in the regular classroom. Fewer kids test at the later grades but I'm guessing that a higher percentage of those who test qualify (no data, just anecdotal observations).
Even though we have experienced benefits from early identification for our kids, I sometimes wish that the identification process were implemented later/differently.
My oldest is an anomoly in that she had a "general intellectual ability" id by 2nd grade but she clearly stood out by that time and we had private IQ scores, WJ-III scores, plus she had SRI Lexile and MAPS scores from school in the 99th percentile. Most of the kids in our district are identified btwn 3rd to 5th grade. I don't see any difference in the kids ided in 5th grade vs. earlier in terms of whether they actually appear to be gifted. On the other hand, the 5th graders who get a GT id are often kids whose parents have been pushing for years for that id and who haven't qualified up to that point, but have been tested repeatedly until a qualifying score was found. Perhaps it is test practice by that time.
