Holding back kids is done more than you'd think. There are several studies on the benefits of holding your 5-year old kid back a year. Basically you get an advantage from an early age at being the best in your class and that helps you throughout your life. I also read a study on NHL players where they looked at their birth dates. Basically, there's a strong bias towards the birth dates of NHL players being close to the leading edge of a school year, so even though they weren't held back a year, they tended to be the oldest students in their given classes. Being the oldest they tend to do better in athletics, and that carried them all the way to the NHL. I do know quite a few immigrant families that say their kids are several years younger than they actually are -- I think that's done more so along the lines that they want their kids to have a better chance of succeeding academically, versus athletics.