I'm no expert but it sounds like autism. If the parents won't do anything, how about tailoring your lessons to methods used for specific disabilities?
One kid I teach is autistic. I found that he likes activities that involve manipulating things with his hands. Matching flashcards to words, using felt leters on a board to spell simple words, and recently I've found a great phonics program he seems to really like working on, and is really good at.
On the other hand, he hates writing, and doesn't respond well to oral instruction, or book-based.
Try getti nyourself a felt board with numbers to do the math problems. being able to physically move them around could help.
As for the parents, I am sure by now they aware of his problems and have their own reasons for not wanting to pursue it any further. It might be touchy to bring up the subject again with the parents. They may find you are intruding. In my Asperger's mind I would research his symptoms and present them with a report complete with suggested solutions, phone numbers of doctors etc, but I've learned that's not really appreciated!
The most you can do is try different methods, and tailor your lessons to suit his strengths. Eventually he'll improve with teh right technique and you'll have the satisfaction of being able to do at least something for him!
Small achievements can really make a difference in anyone's life.
[Modified by: Qof on December 12, 2007 11:07 PM]