My DD's Cog AT composite was about 35 points lower than her WISC GAI. Most of the problem was that it is timed and she has no sense of time and processing speed issues.
The district said they would take outside results like the WISC but I had to inquire about this. Otherwise they would have just given her the Cog AT again the next year.
I also think there is a time limit on outside test results they will consider. They probably won't take anything that's older than the previous school year. So my DS took the WISC but they probably won't accept that when it's time for him to be eligible for g/t.
The GAI can also be dicey in many places- the regulations on FSIQ vs GAI can be vague, and many administrators don't understand GAI. A full psychologist's report is often helpful, but I know people who have encountered roadblocks on this point.
