CogAT can be age-normed or grade-normed. I believe it can also be locally or nationally normed.
It sounds like your DC's test was age-normed, so his/her scores for his/her grade ("grade-normed") could be higher (with a 99%, this could only be seen with an SAS score, which is not always provided to parents) or lower, depending upon his/her age for his/her grade.
The problem with a 99% on the CogAT is that I think it encompasses any SAS score from 135-150 for the CogAT6, for example - quite a wide range. I would have liked to have seen the SAS scores to better understand my DD's score, but this was not provided to us.
HTH!
