Of course if the study is really measuring only the impact of GT programming on average kids, one might be tempted to say, "Who cares?" I'm happy if that's not cost-effective, if limited GT resources should be spent on GT kids. My question was really not whether the GT program and study caught a lot of average-ish kids, but whether the study measured enough above-average-ish kids at the cutoff to make the results meaningful in the intended way. Unfortunately, we don't know anything about the giftedness of the kids at the cutoff; we just know their matrix scores. We certainly can't guess that the scores on that silly matrix map to IQ, and certainly not to intelligence, whatever that is. (Says the guy who skimmed exactly two pages of that report so far.) The study may well be too flawed to be meaningful at all, I guess, although it's not so clear to me just from the logic you've presented here.
It additionally occurred to me that if we were to accept that GT programming should result in higher achievement scores, then a failure to improve achievement scores of kids at the boundary would still be cause for a valid complaint about the overall cost-effectiveness of the program-- it wouldn't matter how gifted those kids were, and it wouldn't be necessary to disprove an effect on more highly gifted kids. That is, the bar being set too low for identification and entry could be a big problem, and such a study might help point that out. And if the GT programming would theoretically result in increased achievement scores for higher-achieving or smarter kids, I see no reason for just assuming that the effect would peter out completely before reaching kids at the cutoff; that would be cause for investigating further instead of making a questionable assumption.
I don't have time to read the whole study. I'm left wondering why, since they must have had data available for the higher achievers too, they would focus just on the boundary kids (ETA: It looks like they must not have had enough data based on attrition rates of high achievers, and the fact that most high achievers stayed in the GT program). To that extent you've heightened my skepticism of the study. Still, a program doesn't have to be a complete waste to be wasteful. Note also the key words "well run" from the OP.
I will have to think further about whether or not gifted programming should result in a measurable effect of some sort. It seems desirable to have some sort of metrics about the success of a program, in addition to reports of happy students, although ordinary achievement test scores might not be the proper metric. I agree with Bostonian that gifted kids deserve to be taught, in addition to deserving to be socially and emotionally happy. I also don't like throwing money down a hole. (Of course, I live in an area with no gifted programs, so the whole discussion, as my most-hated boss would have said, is "mute" for me.)
