I am not in a position to recommend any specific strategies for your autistic spectrum son.
However, in my (rather extensive) research on schooling strategies, it appears that starting formal schooling too early can actually be harmful.
So, what are the alternatives? Again, there is a fairly rich body of research suggesting that we should let our kids play. (Pretty radical idea … not). I suggest you take a look at some of the writings of Dr. Peter Gray.
Lastly, my opinion.
I have come to believe that children learn best when they are learning about things they are interested in, and enjoy. While I don’t have extensive experience with autistic spectrum children, those that I have encountered seem to become engrossed, occasionally in some really fascinating areas. I therefore believe the unschooling approach to learning is very valuable. (Once again, Dr. Peter Gray writes extensively about unschooling).
Okay, I said I was done, but I had another thought, and wandered off on some additional research.
It occurred to me that the Sudbury school system might be appropriate for autistic spectrum children. A quickturned up a number of interesting articles, including this one:
Anyway, the Sudbury type school may be a very helpful and appropriate choice for your son, so is another avenue worth checking out.