I'm so tired of hearing everyone's problems with the CogAT and wish that test would be eliminated. All of the districts around here that use it seem to be quite rigid about it. The g/t coordinator here went so far to say that every subtest on the CogAT needs to line up with the computerized math/reading achievement testing. So if a child qualifies for a g/t program based on an achievement score in math of 98 percent, the cogAT quantitative section would also have to be 98 percent. If they are flagged for a reading score of 98th percentile, the verbal CogAT score would need to be 98th percentile. A high non-verbal score on the CogAT? What achievement test aligns with that? I don't think they thought that far. And in fact they pretty much seem to be making up bizarre rules as they go along. They told me that they would accept outside testing like the WISC but they would need to look at the WISC to make sure the math section of the WISC is at least 98th percentile. DD did "arithmetic" in the working memory section instead of digit span. I can see these geniuses looking at that and saying "Aha! Here's the math section of the WISC! Enter that in the computer!"
I symptathize--it's all very frustrating.
AS for your original question, I'd probably try to show the teacher your outside test scores and say that your DD would appreciate work above grade level. If that doesn't work it's probably not worth the effort at this point just for a few more months of school. I don't know about sending it to the IEP team unless IEPs there address gifted issues. Here none of that is addressed in an IEP and they don't care.