You might also inquire as to what is this "test" that they use to determine giftedness. Is it a test designed for group testing, like the Iowa Basic Skills test or the Cog At test? Or is it a test that is for individual testing? Group testing is aimed more at the average kid or moderately gifted kids and has rather low ceilings. The individual tests, WISC-IV or WJ III, have a higher ceiling.
Our school starts with the tests that fall into the group testing catagory. (They are administered individually, but are aimed at testing the masses). They only go to individual testing if a kid hits the ceiling on the first exams.
Just thought that I would point that out. I also wanted to add that your school sounds wonderful if they let your child float up to different levels for subject acceleration. And schools generally follow the Iowa Acceleration Scale if they choose to think about a whole grade acceleration. Part of that process is asking the child if they want to be accelerated by a whole grade. If the child is comfortable socially and chooses to stay where he is, then the school stops looking into the whole grade acceleration. They also bring in school psychologist to see if your child is emotionally ready for the advancement. It is really a reassuring process that they go through in order to determine if a child should be skipped up a grade or not. If you ever go down the path for whole grade acceleration, then ask your school if they follow the Iowa Acceleration Scale.