I live in a high SES district where the average test scores are at about the 75th percentile. If you assume a normal distribution, this would mean, based on test scores alone, about 25% of the students would qualify for a GT program that has a cutoff at the 90th percentile (which is not uncommon). Add in other ways to get in--teacher recommendations that value conscientiousness and executive function, for example--and you could easily get to 40%. If the average IQ were 115, almost 40% of the students would qualify on test scores.
