"But researchers have studied the effects of kindergarten redshirting and found no evidence it make a significant difference for long-term educational outcomes." (Mead blog) Actually, the cited research says exactly the opposite: "The results of this inquiry revealed...children who began school at a somewhat older age performed better at the start of school, evinced greater improvement over the course of their first years of schooling, and functioned at a more advanced level in third grade than children who began school at a somewhat younger age." The study did not, however, distinguish between effects on boys and girls, so is irrelevant to the question of whether redshirting only boys would better calibrate education to development.