I don't have much advice for you, but I will say that my daughter's CoGAT Quantitative score jumped 40 points (from 110 to 150) between two testings, so I don't really trust that test much anymore.
I don't trust the CogAT either, but I can easily see how it would happen. The test is highly dependent on fluency with math facts, so a kid who gets the facts down to automaticity between the two administrations will very likely do much better.
Of course, this is exactly why I think that the CogAT only picks up a certain type of quantitative aptitude. It has completely missed the type my children possess, which is more of a thoughtful, reflective, problem solving type, and less about quick retrieval of facts.
