I first heard of the Relative Age Effect when reading Jeff Booth's "Price of Tomorrow". In chapter 7 "Who Will Be the Master" Jeff touches on the topic, but – as it is by far not the main point of the book – doesn't go deep down this rabbit hole. Nevertheless he got me interested, and I decided that I'll dig deeper... But i didn't. Not for years.
Then I stumbled across a social media post glancing over the same topic. So I decided it's time to finally explore it. Here's what i found:
What is the Relative Age Effect?
The Relative Age Effect is the uneven distribution of achievement by birth month, caused by age cut‑off dates (mostly) in sports and education. In sports, teams are often grouped by calendar year (cut‑off January 1), so children born in January and December may train together despite being up to 11 months apart in age – a gap that’s negligible for adults but can mean an 18% difference in life experience for a 5‑year‑old.
First noted by Canadian researchers studying Quebec hockey players1, the effect has since been observed in U.S. hockey2, Russian football3, and other sports. Data from 11,000 Russian athletes born after 1980 shows it’s strongest in team sports and especially in childhood.
In education, the cut‑off date usually aligns with the start of the school year, not the calendar year. For example, in the UK, children born in September (just after the cut‑off) are the oldest in their class, while those born in August are the youngest – and data shows September‑born applicants score higher on average when applying to Oxford University.
Why does this happen?
I used to play football professionally and – while I wasn’t the youngest – I also wasn’t the oldest on my team. I often looked up to older teammates and, trying to match their results, I felt I was “playing up” and being stretched by stronger, more skilled peers. For years, I believed that being younger was a privilege.
I was wrong.
In some individual cases, younger players do benefit from that dynamic. But when researchers look at large groups, the data usually points the other way. It comes down to maturity and self‑reinforcing feedback loops:
Sports
- Physical maturity: Even a few extra months can mean more muscle mass, coordination, and stamina in childhood. Coaches often pick the bigger, faster kids for elite squads, which gives them better training, more play time, and more confidence – a feedback loop that compounds over years.
- Early selection bias: Once you’re in the “top” group early, you get more resources and better competition, which accelerates your development compared to peers who didn’t make the cut.
Education
- Cognitive maturity: At age 5 or 6, an 11‑month gap is huge for attention span, vocabulary, and social skills. The oldest in the class (just after the cut‑off date) often start school more “ready to learn,” which can translate into higher test scores and more positive teacher feedback.
- Confidence effect: Early academic success builds self‑belief, which influences participation, leadership, and willingness to take on challenges.
Being the youngest can push some kids to work harder, but it’s a tougher path – you’re competing from behind in size, strength, and maturity. Without exceptional resilience and supportive coaching, the gap is hard to close.
Are kids born mid-year doomed to fall behind?
Not necessarily – even though they start off in a worse position. In both sports and education, the early advantage of being older in your cohort shrinks as physical and cognitive differences level out. By early adulthood, raw maturity gaps are gone – everyone’s fully grown, and other factors – skill, resilience, adaptability – matter more4.
In fact, this effect reverses (to a certain extent) over time. Some studies find that relatively younger athletes who survive the early disadvantage may outperform their older peers later on. They’ve spent years competing against bigger, stronger opponents, which can sharpen skills, mental toughness, and adaptability5. In education, the oldest in the class often do better early on, but the gap narrows – and sometimes disappears – by university or mid‑career.
Whether you were the oldest or youngest in your class or team, your birth month may have shaped your path more than you think – but it doesn’t have to define where you end up.