As a middle school teacher, I highly recommend you wait the extra year. By the time they reach the middle grades, the youngest boys in the class seem wildly immature compared to the oldest ones. And even some of the older boys seem less mature than the girls. There’s a whole concept in education about this called “redshirting”: it’s the idea that younger kids (and boys especially ) be kept from Kindergarten the extra year to allow them to be on-par with the older kids.