This has been on my mind recently, there are lots of threads about it, but I just wanted to share (as far as I can) info about our intake to reassure others, and because I've recently discovered many 'friends' with four-year-old kids and old address books who are ringing me.
Your kid is ready for school if they can interact with others and are cognitively capable of learning. They are not more or less ready if their skills are strongest socially, academically or in terms of self-care. If you have as a parent have helped them to achieve what they are capable of in terms of dealing with others, being happy and willing to learn you've done an ace job. There is no check list, from shoe tying, toilet training or recognising their names. All of that helps, but can be got around, and in the round they can still be ready.
This year we'll have a kid in nappies who is clearly socially and cognitively able to cope, one who we think will cope even though selectively pre-verbal, a few who can't dress themselves, one with ASD who will find interaction hard. And we'll cope. And hopefully they'll learn.