I started my son in kindergarten at 4 years old, the cut-off here in CA isn't until 12/1. There were tons of kids in his class that were Fall birthdays, so Summer doesn't even seem early to me. I think almost every child is ready for K, maybe two years of it, but ready to at least start. love the private K and then on to regular K at the public school idea, but starting K on time or early in my opinion is a wonderful thing for the child as long as there are options for repeating K. In my old school district kids could start with fall b-days, but had to do two years. K is not hard, yes, there is learning, but it is reasonable (I'm sure some schools are different, but for the most part...). First grade is where it is becomes more of an issue. I've also met a few kids who were held back in pre-school and entered K at almost 6, and they seem fine too. I think they would have been ready either way, but they seem happy enough with the younger kids. My pediatrician says new studies show holding kids back isn't a good idea, and younger is better, but who knows. It looks like there are good reasons to do either.