The relative age effect (RAE) and its relationships with maturation, anthropometry, andphysical performance characteristics were examined across a representative sample of English youth soccer development programmes. Birth dates of 1,212 players, chronologically age-grouped (i.e., U9’s-U18’s), representing 17 professional clubs (i.e., playing in Lea-gues 1 & 2) were obtained and categorised into relative age quartiles from the start of theselection year (Q1 = Sep-Nov; Q2 = Dec-Feb; Q3 = Mar-May; Q4 = Jun-Aug). Players weremeasured for somatic maturation and performed a battery of physical tests to determineaerobic fitness (Multi-Stage Fitness Test [MSFT]), Maximal Vertical Jump (MVJ), sprint (10& 20m), and agility (T-Test) performance capabilities. Odds ratio’s (OR) revealed Q1 play-ers were 5.3 times (95% confidence intervals [CI]: 4.08–6.83) more likely to be selectedthan Q4’s, with a particularly strong RAE bias observed in U9 (OR: 5.56) and U13-U16 squads (OR: 5.45–6.13). Multivariate statistical models identified few between quartile dif-ferences in anthropometric and fitness characteristics, and confirmed chronological age-group and estimated age at peak height velocity (APHV) as covariates. Assessment ofpractical significance using magnitude-based inferences demonstrated body size advan-tages in relatively older players (Q1 vs. Q4) that were very-likely small(Effect Size [ES]:0.53–0.57), andlikely to very-likely moderate(ES: 0.62–0.72) in U12 and U14 squads,respectively. Relatively older U12-U14 players also demonstrated small advantages in 10m (ES: 0.31–0.45) and 20m sprint performance (ES: 0.36–0.46). The data identify a strong RAE bias at the entry-point to English soccer developmental programmes. RAE was also stronger circa-PHV, and relatively older players demonstrated anaerobic performance advantages during the pubescent period. Talent selectors should consider motor function and maturation status assessments to avoid premature and unwarranted drop-out of soccer players within youth development programmes.