Hi
I can't give much on Cogat. It seems fairly hard to get much information about the test results. Those are very strong scores. Cogat is not an IQ test, but I would imagine a high achiever but not gifted child would not score that high on Cogat.
It is scored as Zen mentioned on the same type of scale as IQ. Which at least gives some reference to for rarity.
IBST is a grade level achievement test. It is hard to get what level of gifted is going on at 99 percentile on a grade level test. The ceiling is very low for a gifted child. High Achievers with good exposure levels can score 99 on it. I have seen that a lot in our district.
He will looks like a wonderful fit for a self contained gifted program. You may actually find its not enough either depending on your ds and the selectiveness of the program. You are probably going to have trouble getting a good handle on his level of Giftedness with either one of those test. Individual IQ testing or above grade level testing would likely be far more informative for you.
