I think parents of borderline age children should be able to choose their child's school year. Not just choose to delay entry, but choose the year group.
My youngest is an end of August born - a week later and she would have been a whole school year below. To add to that she is tiny for her age, and young emotionally. She just does not fit with her year group. She is now Year 6, and every single one of her friends is year 5 or 4. The thought of her going to secondary school next September is just appalling - she's still sat at home playing with her My Little Ponys and we are looking at choosing secondaries!
When she started in reception she would have been nowhere near ready in the September. At only a week over 4, she was still having an afternoon nap. We delayed her entry until January, but I still had to take the pushchair up to school to collect her and I still couln't find school clothes small enough to fit. Her starting school so young was a ridiculous idea for her, quite frankly.
She is a bright child, but at only 4 there was no way she could compete with children in her class who were a whole year older, all bar a week or two. She kept saying "Mummy, I'm not as clever as the other children, I can't do any of the things they do." I had to keep on and on saying "You are just as clever, you are just much, much younger." Unfortunately schools don't make this clear to the summer borns. They are just all lumped together. My eldest was 7 and a half when she did her Y2 SATS, my youngest was still 6. How is that a fair comparison?
She has easily caught up academically now, but lots of children don't. And I still look at her and think she will leave Primary at 10, sit GCSEs at 15, sit A levels at 17 - it still seems massively unfair. If I had had the choice I would have kept her back to the year below where she would be a much better fit. Yet the ironic thing is I have friends with September born children who would be better in the year above.
We need choice. Choice to keep your child out of school a year and then have to plunge them straight into year 1 is no choice at all.