Was it the school psych who said he wasn't dysgraphic?
Most school psychologists aren't certified to practice medicine (diagnosing disease), instead they are certified by the Department of Education. If you have a diagnosis from a medical professional, they can't dispute that (although they might try!).
If your son has been diagnosed with a disability (dysgraphia), and the district is not respecting his right to accommodations, gently threaten to file a complaint with the Office of Civil Rights. This threatens all the school's federal funding, and school employees tend to take you a bit more seriously then.
I'd wait to pull out the big guns until you have tried everything else though.
Try not to burn any bridges.
