Big mistake. For one thing, New York has these mandatory pre-schools, so all his classmates had a year of standing in lines, following schedules, and listening to strange adults, while these concepts were completely new to him.

More important though, he wasn't ready. He'd do fine for half a day, despite his lack of previous experience, then he'd be tired and irritable after lunch, and in consequence he'd get in trouble for something almost every day. Not good if you're trying to build a love for education.

I suspect if you look deeper, you'll find that a lot of the "expelled" kids were kids whose parents were told, "they're not ready - give them another year at home". It could be that they came to school miserable every day because they didn't want to be separated from Mommy - you're dealing with 4 year olds at the pre-k level, after all. It could be they don't have the stamina to handle a structured program yet - they need their own naps and meals and snacks at the times their body says, and not when the schedule says it's time. The first year of schooling should be a joy, not a trial. It is sometimes better to wait and try later than to stubbornly tweak the program while the kid's love for the school adventure is being eroded by negative experiences.

One very likely possibility is that those who ran into problems had never been outside of the home setting before. My eldest did three years of daycare before ever hitting kindergarten - not something we wanted or would recommend, exigent circumstances. She took the transition to kindergarten like a duck to water, but the early settling into day care was far easier for her than my son's later attempt at kindergarten was for him, mainly I think because she was so young - it was just a different kind of family for her and ALL rules were new, while my boy had to contend with the fact that the rules and patterns of behavior that he had learned at home weren't applicable at school.