In most European and American schools the academic year begins in September—a schedule originally devised to enable children to work on their family’s farms during peak agriculture months while still receiving a compulsory education.
This structure means that kids born before the cut-off date of August 31st are almost a full year younger than their peers who were born September 1st of the previous year. When you’re a child, this means a substantial difference in terms of intellectual and physical development.
September babies have a 12-month head start on their August counterparts, so they’re often perceived as smarter and more able. This, in turn, garners them additional attention and resources in the classroom; teachers give special attention to the students who show the most promise, which only serves to widen the gap further.
As Malcolm Gladwell explains in his book Outliers: The Story of Success: If you make a decision about who is good and who is not good at an early age; if you separate the ‘talented’ from the ‘untalented’; and if you provide the ‘talented’ with a superior experience, then you’re going to end up giving a huge advantage to that small group of people born closest to the cutoff date.”
This effect, known as “month of birth bias,” was the subject of a recent study into school starting age. Researchers confirmed that individuals with September birthdays do better at school, have greater academic success at college, and have significantly lower rates of incarceration than June, July and August-born individuals.
That being said, there are, of course, innumerable anomalies. Just because you’re a summer baby doesn’t mean you won’t be CEO some day.