Reply from Malcolm Gladwell when asked about a child’s birth month being an advantage (emphasis mine):
Question: In Outliers, you discuss why a hugely disproportionate number of professional hockey and soccer players are born in January, February and March. I can’t begin to imagine how many to-be parents you influenced to try and have their offspring be born in those months!
MG: Well, I have heard that some parents took that to heart. I should add, however, that when it comes to academic achievement, the problem of being the youngest in class is most pronounced for kids with other challenges. If you are from a lower-income, broken home, and you have a learning disability, AND you are the youngest, that’s too much to ask. For the typical middle-class kid from a good, well-educated family, I’m not sure it matters so much. In other words, the kinds of people who took that message to heart are probably the people who least needed to take it to heart.