During the time I worked for KCS I saw three distinct phases.
During the 80's, KCS had transition classes which served as a bridge between kindergarten and first grade. Teachers could speak freely about the advantages of kids waiting to start kindergarten.
In the 90's, KCS phased out transition classes and kindergarten teachers were basically somewhat silenced. There was an under lying understanding that teachers weren't supposed to talk to parents about holding their kids back if their birthday was too close to the cutoff.
This current phase I call the "don't ask don't tell period." In recent years--and even again this week--I have had parents say they did not know that they didn't have to start their child according to their birthday. Parents, you CAN hold your child out a year and let them mature.
As an educator for 40+ years, a mother of four, and grandmother of 12, I can speak both professionally and personally to this. I had two sons: one with a July birthday and one with an August birthday. I made the mistake to start them and not to wait. Later--with much difficulty--we corrected the decision but not without some drastic measures.
From life lessons learned, our oldest grandson (who has a June birthday) waited a year. This year I have three more grandchildren that qualify to go to kindergarten based on the age set by the state, but NONE of them will be starting. Two of them have May birthdays and one has a July birthday.
As a first grade teacher for 13 years, and a kindergarten teacher for ten, there is a whole lot more I could say professionally. But because of time and space I wont. However, if you would like to discuss this further, email or call me. Remember just because your child can start, does NOT mean your child should.