I have recently returned from a country where children did not start formal eduction (the 3 R's) until the year they turned six. (Although prior to that there was Nursery provision which concentrated on such things as pencil control, listening, language, motor and social skills and therefore smoothed the path to formal schooling)
Comparing them with my UK educated children, a year later they were at the same standard, having learned with much less effort and angst because many more of them were more mature and ready. There was less of a gap between the genders, too and where their birthday fell within the academic year also seemed less relevant.
Perhaps ours are starting formal school too young?