@clockover 'As far as you know' isn't that far though, is it? Just because only one girl cried when you got to school doesn't mean everyone else was ok. It's not just about going to school. There is being at school. The thing about 'back in the 50s we did x' is that we have progressed over the years because through research, test and observation we know children perform/cope/manage better if they have the chance to develop socially before getting thrown into school
Well I was at school with them for years so if it had some dire consequence it didn't show up for quite a while.
One of my GC started school in September, I was asking her mother how it had gone, she said she missed her nursery so much, found it very strange that teachers don't give you a hug or sit you on their knee if you are upset. Didn't sound much easier than it was for us.
Is there any research about how the August born cope compared to the September born, they aren't one homogenous mass they are individuals with some being considerably older than others (11 months 3 weeks is a big gap at the age) some are going to be brighter or more confident, some will be big for their age some will be tiny, some have brothers and sisters. I dont think we can assume they are all the same and the OP knows her child far better than anyone on here, whatever research they have done.
Mine started school at 9, no problems, both passed the 11 plus 2 years later, both got first class honours degrees, both have post grad qualifications, both in happy relationships with good jobs. That might not work for others but they are my kids and I, with DH, made the decision that was best for them.