Your decision will have long ranging effects. Once your son starts public school, he will most likely continue in the system nonstop for thirteen years. So in making a decision about when to start school, you are not making a decision about kindergarten alone, but about a thirteen year career. So those children who are lucky enough to have winter birthdays can handle this curriculum with relative ease while those on the younger side may have difficulty. If they do manage the work, they often have no energy left over to participate in social life with friends and family.
Stress can become a way of life.
The rest of the grades follow suit, and the trend is toward a more rigorous curriculum at all levels. Homework is mandatory at younger and younger grades and social promotion is no longer an option in many states. So a child who is working beyond his capacity eventually falls behind and is retained or is placed on support services. Children who start later rather than early are usually successful, and have very little retention, therefore avoiding an unfortunate stigma weave never seemed able to eliminate. After third grade, many of the children who are developmentally young also develop social problems.