The CogAT and OLSAT are similar types of group ability tests. My HG+ child who is not twice exceptional had similar results on MAPs and ITBS tests in elementary (3rd and 4th). I'd say that I'd lean toward him being gifted but, like Inky, I'd want to see ability scores as well and how his achievement continues as he gets older. Achievement scores can be higher than ability in hard workers and are sometimes higher than expected especially in early elementary. However, 99th in all domains on MAPs certainly points toward a good possibility that it may be more than high achiever syndrome ;-)!
I would offer the personal opinion that I wouldn't assume that he isn't gifted if his CogAT scores aren't in the gifted range. Group tests aren't always the best measure of gifted kids. Hoagie's has a note about a study on the OLSAT that found a negative correlation with IQ for gifted children and especially HG kids. I've known kids who come out in the mid 90s on group tests who've had individual IQ tests later administered (and sometime more than one IQ test) and the IQ test scores were nowhere near that high. I've also known kids (my 2e one included) who had high-ish group test scores but not gifted scores and who had HG-PG individual IQ scores.
If his achievement is that high, he should be offered some sort of acceleration such as subject acceleration for now. If he continues to outpace his peers and the ability scores are gifted as well, placement in a full time gifted program or grade skipping may be something to consider later.
eta: I was noticing in your prior posts that it looks like you had some private testing done a year and a half ago. Did that give you any further info to sort this out and did they do IQ testing at that time? IQ scores, especially from that young, aren't set in stone certainly but if they did test IQ it might give you more to go on or more with which to advocate. Can we safely assume that the school never came through on the grade skip they were considering at that time?
