I have a may baby. She is exceptionally bright (18 months to 2years ahead of her peers). We knew that when she was at preschool. She was also very sensitive and no great at dealing with situations where she felt 'attacked'. We ended up holding her back. There were a whole host of social reasons for her, and her preschool teachers felt it best for her. the two private schools I had her booked into wanted her straight away due to her academics.
I did find a school readiness checklist and I felt she was ready but they could see things that I just didn't.
It was THE best thing I have ever done for her. she has gone from the likeable easily led kid who had lots of friends, to the confident kid who makes good friends easily with all kids and is a great leader who the other kids look up to. The one who couldn't bear to have anyone look at her to the kid who proudly went up to collect her academic award at the end of her first year. She deals much better with all the situations school throws at her than I could have hoped.

My concern was that she would struggle and she would have to repeat. I've heard it happening so often and I didn't want that for her.

A friend of mine is currently going through this for Her April baby. She sees that he an 'keep up' with all the other kids that are going to school and are his friends. She can't see that even though he can create elaborate games he still plays alongside other kids rather than collaborative play, that he cannot sit and listen to the simplest instructions, that he cannot deal with playground spats and needs an adult to deal with them but he cannot ask for help and just cries and walks away. She's defensive that they've even suggested he shouldn't go to school. But there's just some stuff she just can't be objective about as her dh wants her to go back to work 5days a week.

Now I'm not suggesting in the slightest that you're like that (hell you wouldn't ask here if you were ). You just asked for both experiences.

It is the hardest decision I've ever had to make.