Hi,
I have 3 sons on the Autism spectrum, all are high functioning PDD-NOS or Aspergers. This is a very real issue and very common with these children. Most of them are extremely gifted in math and do not do the work because they can see it just by looking at the problem. Believe me we have dealt with this... My oldest son was doing Alg.I in 6th gr.
If you pressure these kids to do something it's not going to work, period.... Either these kids explode or they melt and internalize. My son had a major melt down, crash and burn totally in 7th. I know... I see it everyday. You can only push these kids so far so fast.
First, I would suggest cutting down on the amount of math problems the student is given. They also don't like to put names, dates and any other labels on their papers. Second call another IEP and make sure everyone is trained in High Functioning Autism, not low functioning. Make sure that all are aware of this particular students uniqueness. No two Aspies are the same. Next show the student the value of putting the work down..... For example use the example of the space shuttle crash being r/t a missing negative sign. That's all it takes.... Help them see value in showing the work and then gradually implement. Slow is best with these kids. In the meantime if the math teacher is thinking he's cheating he can do his tests away from all others in a resource room. Give the student a break, they need it or their anxiety levels will sky rocket. You may think they struggle at school but when these kids come home they let off all their steam and believe me they vent. Things that are insignificant to the rest of the world are major to these children.
Most of all encourage the postives and any progress in the direction you are seeking. Any negative vibes of any kind can send these kids in a tail spin that they can't stop.
HTH,
Sue