The Relative Age Effect in Basketball: Why Your Child's Birth Month Matters

If your child was born in the second half of the year and has been overlooked at representative tryouts, it might not be about talent. Research consistently shows a powerful hidden bias in youth sport selection called the Relative Age Effect (RAE), and basketball is no exception.

What Is the Relative Age Effect?

In most basketball associations, players are grouped by calendar year. A child born in January competes in the same age group as a child born in December of the same year. That is nearly 12 months of physical and cognitive development difference.

At ages 10 to 14, this gap is enormous. The January-born player may be taller, stronger, faster, and more coordinated, not because they are more talented, but simply because they are more physically mature. Coaches and selectors, often unconsciously, mistake maturity for ability.

What Does the Research Say?

A 2017 study of over 7,000 young Polish basketball players found a significant RAE across all age groups for both boys and girls. Players born in the first quarter of the year were dramatically overrepresented on elite teams, while later-born players were systematically excluded. The effect was strongest in U16 boys, where the physical maturity gap is at its peak.

The same study found that in U14 boys, earlier-born players had significantly higher match statistics and performance ratings. But this advantage was driven by physical maturity, not skill.

A 2021 study by Kelly and colleagues examined England Basketball's national talent pathway and found strong RAE in selection. Earlier-born players were heavily favoured in the pathway, even though birth quarter had no significant relationship with successfully transitioning to senior professional basketball.

Most recently, a 2025 French study of 131 elite youth basketball players tracked who went on to achieve at higher levels. They identified four distinct athletic profiles and found that the Relative Age Effect influenced initial selection, but did not predict long-term success. Players who were selected later or initially overlooked often caught up and surpassed their earlier-born peers.

Why This Matters for Your Child

If your child is born in the later months of the selection year, they face a real structural disadvantage in the talent identification process. This does not mean they are less talented. It means the system is biased toward early physical maturity.

Understanding this can help in several ways:

• Reframe setbacks: Not being selected at U12 or U14 does not mean your child is not good enough. It may mean they have not physically matured yet. Research shows that juvenile success does not correlate with senior success. Only 4% of world-class athletes had international results at age 14.

• Focus on skill development: Physical advantages fade as everyone catches up through puberty. Skills, basketball IQ, and work ethic are permanent. Invest in these.

• Build resilience: Players who face early setbacks and respond with harder work often develop stronger mental qualities than those who coast on early physical advantages.

• Be patient: Development is not linear. The best 12-year-old is rarely the best 18-year-old.

What Should Coaches Do?

Research from selection psychology suggests several improvements coaches can make:

• Use structured assessment criteria rather than subjective impressions. Studies show that coaches who rely on overall impressions are prone to significant biases, including favouring taller, more physically mature players.

• Consider biological age alongside chronological age. Two players born in the same year can be at completely different stages of physical development.

• Focus on skill samples over isolated tests. Research shows that observing players in game-like situations (small-sided games) predicts future performance better than isolated sprint or agility tests.

• Track progress over time rather than making one-off selections. A player's trajectory of improvement is more predictive of future success than a single snapshot.

A Personal Note

This topic is personal for me. My daughter was born in October and has always been small for her age. She experienced the Relative Age Effect firsthand through several selection disappointments during her junior career. Being overlooked when you know you can play is hard for any young athlete.

But those setbacks built something that early selection could not: resilience, work ethic, and an unshakeable determination to let her performances do the talking. She went on to earn a full-ride D1 scholarship and was invited to the NBA Basketball Without Borders international camp. The system initially worked against her. She outworked it.

If your child is going through something similar, keep the faith. The research is clear: early selection does not predict long-term success. Hard work, skill development, and resilience do.

References

• Rubajczyk, K., et al. (2017). Doubly Disadvantaged? The Relative Age Effect in Poland's Basketball Players. *Journal of Sports Science and Medicine*, 16, 280-285.
• Kelly, A.L., et al. (2021). Relative Age Effects in Basketball: Exploring Selection and Transition in a National Talent Pathway. *Sports*, 9(7), 101.
• Irid, Y., et al. (2025). Impact of athletic profiles and the relative age effect on future achievement levels of young basketball players. *Frontiers in Sports and Active Living*, 7, 1616800.