My son (like Kate's, 10 and DYS) began getting social skills and behavioral training in 2nd grade, when he got a formal diagnosis of Asperger's from the school. I don't know what ABA is, so I don't know if it was that. He has done so well with all the things the school does, and an outside counselor on occasion, that we dropped his IEP this year because he doesn't appear to need it anymore. However, I think he would have done even better if he had started earlier. I "knew" he was autistic from before he was 2, but refused to label him and insisted he was just a smart kid and there was nothing "wrong" with him. His preschool director tried to suggest it when he was 4 and 5, and I still refused. It wasn't until 2nd grade when it really started getting out of hand, that I finally acknowledged it and the school went to work for him.
I would recommend starting the behavioral and social skills training as soon as he can possibly understand it and take advantage of it, which is probably now. It can make a world of difference.
Don't let them tie the advanced classes to the behavior, though -- that can and must be worked around. Being in classes that are below his abilities can easily contribute behavior problems of its own, regardless of any level of autism.
