I know that CogAT is an unpopular test around here, but I think that if you realize its limitations, it might have some value for some DC. FWIW, DD's CogAT strengths matched up with her WISC strengths (as well as the strengths I have always observed). She scored extremely high in the verbal section of the CogAT (possibly hit the ceiling from the limited data from the school) and had an extremely high VCI on the WISC. DD's CogAT placed her in the 99%, and DD's WISC scores were well beyond >99% (but I do not think the CogAT is designed to determine LOG). I do think that CogAT's "IQ-looking numbers" typically UNDERESTIMATE IQ in most DC (a CogAT SAS will usually be lower than a WISC FSIQ or GAI).
If the CogAT scores appear to have captured your DS's abilities, I would not discount it! I would absolutely use them for advocating - the school would not have given him the test if they felt it was meaningless, so it might be very useful for you/him. Different children shine on different tests - it is great that you have something to demonstrate your DS's strengths!
