I agree that there is a certain unfairness in testing by grade level, and it works to the disadvantage of kids who have been grade skipped.

However, while it seems unfair to those kids, it does make sense. It's the kids in the same grade level (and NOT the kids of the same age) whom they are going to be compared to when they apply to college. Unfortunately, that's one of the disadvantages of grade skipping. By doing so, you are acknowledging that from then on your child will compete with, and be compared to, the children in their new grade.