My son's school used a combination of the post test, the previous year's standardized testing, the previous year's school testing for placement in gifted IQ, score and my outside achievement testing. We were really looking at just math acceleration. The first no I got was just looking at the post test and his worst area was explaining his answer. We kept gathering data and made our group decision with all that data.
But that is a big skill and not specific to on grade level work. My counter to that objection was like finding the main idea is a skill you can work on with a sixth grade book or a 4th grade book and if everything else is factored in might as well work in on that with a book at the correct level...same thing for math...if explaining your answer is the problem area for a child, it is easier to explain a difficult problem rather than 2 + 1= 3.
