you are unlikely to find a preschool that will be academically challenging for him. I agree with the poster that suggested a play based program.
This is one of the only places on the internet where your experience is common, and the more I interact with parents of my daughter's age mates, the more i realize how different she is from them. And her difference is not celebrated, which is an additional challenge.
I would ask about the accommodations they can offer. Mine will "accelerate" her after she turns 3, as there are laws that dictates the ages that can interact in center based daycare. After three, she will be permitted to float around to different classrooms.
