The influence of relative age and biological maturation on player selection in the Scottish football associations Club Academy Scotland.

Relative age and biological maturation significantly impact talent identification and development in football, with professional academies often favouring relatively older and early maturing players. This study investigated these biases across Club Academy Scotland (CAS). The biological maturation of 1,011 players (U10-U18) across 12 CAS academies was assessed using the Khamis-Roche method. One-sided t-tests were conducted to test the null hypotheses that the true mean was 0.5 (relative age) and 0 (biological age - chronological age [BA-CA]). A significant bias favouring early maturing players emerged from U12. The BA-CA offset effect sizes ranged from small (U12, Hedges' g = 0.22) to large (U18, Hedges' g = 1.44). A relative age effect was statistically significant across most groups, with a large effect in U10 (Hedges g = 1.19) but smaller effects in all other groups (Hedges g = 0.16-0.41). This study demonstrated that a RAE exists within professional Scottish football academies, albeit to a small-to-moderate degree, but a larger bias towards earlier developing players exists from U12 and increases in magnitude with each age group. Regular monitoring of biological maturation is essential to address this bias, maximise the talent pool from Scotland's relatively small population, and support developmentally appropriate training programmes in CAS academies.