The difference is holding back a child for sports reasons is driven by parents whereas holding back a child for educational reasons is normally school driven-but with the permission of parents. At least in most school districts holding a student back for sports reasons is not as easy as it seems. Not only does it affect the curve especially since boys don't mature as fast as girls, but it requires the involvement of teachers, Principals, parents. Problem is most Principals don't want to challenge a parents decision based on sports and simply not resist.
