Would they accept a test from a private testing provider (i.e. school psychologist) in your area? Our school system requires minimum standards on testing but you can have the testing done on your own; I think sometimes that some of the school psychologists who work for the system have a vested interest in not necessarily finding gifted kids (i.e. they then have to provide services, which are expensive). A private provider might be able to provide insight into why he doesn't test higher (certainly sounds as though he should). I also don't know if there might be other tests which would give you a better perspective on his strengths and weaknesses (e.g. KeyMath3).

Good luck. Sounds frustrating!