It is so interesting to read about the academic kindergartens. DS has an 8/31 birthday (in a state with an 8/31 cutoff) and we sent him the year he was "supposed" to go. We had comments when he was 2 about how we should hold him back because young boys just did poorly.
I don't think DS learned anything academic in kindergarten, though most of the year was great for him. We put him in 1/2 day, though, so that makes a difference. Not because it was less academic, but because it gave him more time outside of school.
It seems to be common knowledge in our district that many summer boys are redshirted. But the reality does not seem so clear to me.
In DS's kinder there was no one who had already turned 6 when the year started, but one child who did not turn 5 until November (early entrance). In his 1st grade class there was one child who had started late (turned 7 in August, a girl) but also a child who didn't turn 6 until October. Now, in 2nd grade DS is in a 1st/2nd grade split. There is a boy 1st grader who is older than DS (late entrance) and a girl 2nd grader who is younger (only by 9 days, but over the line--- early entrance).
DD's classes have been the same. She was homeschooled and started public school in 2nd grade at 6 years old (January birthday after the cutoff--- so 4 months younger than "standard"). In her first class (1st/2nd) there was a child with a December birthday (early entrance 1st grade--- he was only 5) and a girl in her 2nd grade class that was younger than her. In her 3rd grade class there was a child who was actually two years ahead (1 full year and like 7 days) and a child who was started a year late. Now, in 5th grade she is the youngest, but the oldest is once again someone who is slightly old.
My point? There is actually a lot more age variation *in our district at least* than is acknowledged. While "everyone" knows that you start boys late, no one seems to really acknowledge that there are at least as many starting early and way, way more that just go on time.
IMO, you need to do what seems right for right now and be willing to change in the future. Both my kids are young for the age and if I felt they would be better served being a year back, that is what we would do. Honestly, I really feel like my DD's situation was ideal---- homeschooled for K & 1st and then put in the correct grade at that point, when she was more ready for a full day of school.
Writing is DS's major challenge (not content, but keeping it neat for long paragraphs) and I wonder if he would have an easier time in 1st instead of 2nd. That said, most of his other subject would be way too easy if he was in 1st instead.
Personally, my philosophy is to send the kid to school "on time" unless you have a concern specific to *that child.* Not what might happen to that child in 10 years, or when puberty hits, or what the neighbor says is common for other ______ kids, but for that child. I'm not going to sacrifice the appropriate fit *now* for possibiblites in the future.