It sounds like you're going to have an uphill struggle. Which usually means you've already lost. At least until next year or whenever you get a new teacher. The schools really don't have to do anything they don't want to. And any attempts to force the issue will usually be counter productive. In the end you're working with people, and you have to find the way to tap into each individual's motivations.
I'm not sure of the jargon in your state, but here we talk about establishing "present levels of performance". Try to find a way to get the teacher or school to evaluate your child's current level of mathematical performance. Try to get them to stick to objective tests rather than subjective opinions or homegrown tests. Don't expect them to perform nationally normed standardized testing, or expect them to accept any independently performed testing. This would be more scientifically accurate and meaningful, but schools don't tend to like the advice of independent experts. You might however be able to get them to use the assessment tests that are provided with most of the major brands of standard math cirriculum.
Once you've established where your child is at, encourage the idea that your child should not be force to work on material for which he has already demonstrated mastery. You'll have to negotiate both those terms carefully: "demonstrate" and "mastery". Make sure that there are regular opportunities to demonstrate mastery. Your best bet is you use assessment testing provided from the standard cirriculum and allow them to require a score of 90% or better.
None of this really helps if there is no provision made to instruct your child at an appropriate level or pace.
As Ania suggested, I'd try to get your child enrolled in ALEKS. It is relatively inexpensive and appears to be somewhat accepted within the education establishment. EPGY is excellent and a bit more rigorous, but a whole lot more expensive.
If all else fails, you really have very few options outside of changing schools or homeschooling.
