Well, as this thread has come back to life again, I may as well send a further report from the summer-born trenches.....only it's all good news .
DS2 is now 4.10. He was one of about 7 summer-borns in his original year group. The other five or six summer-borns from his original year-group have gone into reception and done just fine. It's a good school, with sensitivity to the effect of age-differences. The staff have adjusted the curriculum and they aren't pushing the boys (especially) on the reading and writing front - just gently encouraging it. And they make allowances for the extra tiredness that children this young are likely to experience.
DS2 was the exception. His language and social communication were far too far behind for him to access the curriculum or have any meaningful peer relationships in his original year group. We therefore refused to send him to school at 4.0 and took advantage of Bradford LEA's then-policy of allowing him to start reception at 5.0 with his entire education to be offset by a year. This has transformed his life chances and I'm very, very proud of myself for fighting for this result.
Hindsight is a wonderful thing, and now it's quite easy even for the people who thought my decision was peculiar to see how important it was. DS2's language has caught up and he can now answer questions well enough to be able to access the curriculum. But what's even more important is that he has been able to practice his nascent social communication skills with the right peers. No teacher in the world could have made him a true peer of the other August-borns in the original class, none of whom were particularly immature for their birth year and month. He needed to practice social skills with children 6 months to a year younger. Having done that under the guidance of a skilful nursery manager, he has blossomed, and now he is "one of the gang" in his nursery community.
Perhaps 9 out of 10 summer-born children just need an extra bit of thought from parents and some good adjustments in the classroom for a few years in order to thrive (though lots of them don't get this....). But if your child is potentially the tenth - the one who won't reach his potential unless he gets a chance to change peer group, then it is absolutely crucial that exceptions be made. And even Jim Rose - once we pinned him down on this forum - admitted that he had never intended there to be no exceptions to the rule.
PS, note to David Cameron. You have spent perhaps £1000 on an extra year's nursery for DS2. You have probably saved about £10,000 in professionals' time, statementing processes, tribunals and 1-to-1 support staff: and that's just in one year.