In Finland, whose educational system has some of the best results in the developed world, kids don't start institutionalized schooling until age 7. Contrast that with the United States, where we often have our kids in full-time day care within months of birth and start academic preparation in an "institutionalized" preschool by age 3.
Apparently, at least 9% of kids are held back from kindergarten. And mostly for behavioral reasons -- they are not yet ready to sit still and pay attention, etc. What makes us think that kids should be ready to do that kind of stuff at age 5? Even the few that are able to do it, do we really believe that is the best learning environment for the typical 5-year-old?
I have a proposal. Let's encourage parents to homeschool their kids for kindergarten. Maybe even first grade. Homeschool at that age is easy; most good parents have been "homeschooling" them for a couple of years already. All the basic skills that kids are supposed to learn at that time can be taught just as well -- and maybe even better -- in a casual, unstructured environment. And children won't be stressed out by unrealistic behavioral expectations being placed on them.
I bet that more parents would be on board with this than you think. There are many moms who struggle with the decision to put their kid on that kindergarten bus -- deep down, I think they know that their 5-year-old needs to be with them a little longer, but they don't trust their own instincts for fear of looking overprotective. Give folks permission to keep their kids home a little longer, and some direction and resources for doing it well, and they'll be on board.
Schools will need less early elementary teachers, which means those teachers can teach older grades, which facilitates better learning environments there, too. Elementary classes in Finland have 2-3 teachers in them. How much more individual attention can a child get in a room like that?
Furthermore, parents who have started out the learning process with their own kids are more likely to continue to be involved later, rather than just handing their children over to the schools blindly. And it's all voluntary. Parents not willing or able to do it can still put their kids on the kindergarten bus.
I like this idea. A lot.