We used preschool as a place to learn about interacting with other kids that may not be the same, following the teachers, becoming more comfortable in groups where he couldn't be right next to me etc. Socially at 3 it was great with children 6-18 months older, this year with peers not so good. It made our decision to grade skip into gr 1 next year easier! Academically we knew there was never going to be a great fit given he was reading fluently before he started at 3.