QUOTE(Jane S @ May 12 2009, 04:08 PM)

It all depends where is placed on the autistic spectrum. Autism and Aspergers are very similary, with higher levels of intellectual function associated with Aspergers. It is usually males who have this condition, in fact it can be considered a highly extreme form of the male brain. People with autism usually have one thing which they are fascinated by and they use to put shape and order to their world. They are frightened of the world at large, and in order to feel safe they create their different world, governed by the rules they feel are safer, for them. If music is this lad's chosen interest, it can be used to help him integrate with others in his immediate sphere. If he doesn't want to learn to read music, don't push it, concentrate on learning by ear, aural skills, and when possible relate it to a written/printed resource or something physical about the piano. The key is not to give him challenges which make he feel threatened. When he knows he can trust you, then introduce reading music, in small bit sized chunks. Find out what else he is interested in and try and relate your teaching to those interests. If he rejects your ideas, don't take it personally, he can't help it and is probably unable to incoporate the new idea with the world he has created. Don't threaten his world, enhance it, slowly.
He will be petrified of new situations, so it is essential to take your time to let him to get to know you. Things which are constant will appeal. Perhaps when you first meet him you could ask him to show you what he can do with the piano. Also get as much information from the mother about what works, and CRUCIALLY, what is unlikely to work or could trigger a withdrawal.
You need to be aware that he is so scared that he will, effectively, manipulate you. This is part and parcel, and not directed at you in any way, even if he presents this as the case. Remember, he is very vulnerable. The key to success here is, patience, patience, and more patience.
If this doesn't fit in with what you already know about him, give me what information you can (discretely), and I'll see if I can come up with something else.
I think this is BRILLIANT advice and meshes EXACTLY with what I'd say too. Just to add though that you might need more than 1 lesson to really assess the situation as new situations can be especially trying for autistic children. Just being with you ( and assuming you are teaching from your place) in your environment could be very difficult for him. Some (Many?) autistic people thrive on an EXACT routine. So down to exactly where things are placed etc and anything even slightly different to that may make them very uncomfortable and set them off on a meltdown or a withdrawal - depending on how the individual reacts.
All the best in this venture.