They did a similar study about sports expertise. Being born at the wrong time makes you less likely to become a sports star, because the kids who are nominally your "peers" are physically superior, and it creates the perception that you are not as skilled. Pretty rough deal.
I believe RadioLab touched upon this in their recent podcast "Secrets of Success". My memory is a bit fuzzy on the details, but IIRC they interviewed someone who noticed that most hockey teams were made up of players that were born in the first few months of the year.
I guess parents can turbocharge their kids's future by holding them back a year, so they'll be the biggest, strongest, and most mature kids in the class.
