One of the most intriguing things I learned from the book Outliers a few years ago was the Relative Age Effect (RAE). Malcolm Gladwell observed that most (40%) of the best hockey players in Canada are born between January and March.
Because the cut-off date for hockey in Canada is January 1, kids born on January 1 will play with those born on December 31 in the same year. However, the earlier-born kids will have an extra year of growth and development. Players with January birthdays are likely stronger, taller, and more coordinated. Therefore, they are more likely to be selected for talented programs with better training due to this slight advantage. Better training will make them play better. Consequently, they are more likely to be chosen for talented programs again at the next level. This accumulated advantage (Matthew effect) leads to the phenomenon that most of the best hockey players are born in the year's first quarter.
Over ten years later, Malcolm Gladwell experimented in the classroom of Wharton Business School to evaluate the same effect on education. What's the privilege that gets those students in this super competitive ivy league school? Through a survey, Malcolm found that the Relative Age Effect also applied to education. The birth months of the students also follow an odd distribution, and most students in the class have birth months close to the cut-off date. You can watch the whole experiment here.
By Steve Lawrence - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=44416666