What is the success rate of retention for the reason of developmental immaturity in Pre-K?

I was a pre-K teacher and would guess the success rate is very high if a child is held back because of maturity or developmental concerns. Pre-K is all about listening and cooperating and sitting still and getting along with others. It is often a child's first experience in a structured environment. Holding a child back has always been a good thing, to my knowledge.

Your local library should be able to provide statistics and studies regarding this situation. Their ERIC database should be very helpful to you.