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Unfortunately, imho, I think it is backfiring. All the kids being held back aren't being given a leg up, but those that go on time are being pushed down a rung. Too many are held back. And that is why kids seem more immature, even when they are actually on target--most of them around kids that are a year or more older. I think that is also why K is much more like 1st grade. I personally like the districts are not allowing red shirting and maybe offering developmental K or pre-first. I say start them at 5 and given them K back!!
Yes! Give the ones who go "on time" a fighting chance. It isn't fair to them that their peers are a year older. If there is actually a measurable reason, let them stay back. But all, I mean ALL, of the parents I know who have redshirted their kids do it because they want them to be bigger for sports. I will never understand why that's allowed, the rule is so vague, you can't even fight it.
Really, do you want your child to be the first one to have a driver's license? Everyone begging him/her to be the one to drive everywhere? Do we want them hanging out with kids who are less mature? Really?
As a retired teacher, the nightmare it poses for the teachers is unbelievable. The vast range of abilities and maturity dramatically impacts everyone's classroom experience and creates so much more work for the teacher. Is that really what we want?
I realize this isn't the popular answer here, but I just wanted to offer a few other things to consider.
As far as planning a baby to fall w/in a certain month for kindergarten planning... good luck with that.

Just relax and see what happens. You have a long road of parenting to get through before you need to make any academic decisions. (Sleepless nights, diaper changes, introducing solid foods one at a time, sleeping through the night, crawing, walking, talking, potty training...boy I'm getting tired just thinking about it all!

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Just enjoy, you'll do just fine! Kindergarten will come soon enough, but for now, first things first.