Differences in biological maturity status (BMS) during puberty may advantage biologically older players within selection processes. This study examined maturity-related differences across multi-stage selection procedures, playing positions, and the relationship between BMS and team performance within the German Football Association`s U15 national selection tournaments. Anthropometric measurements were collected from N = 695 male regional association team players (M = 14.1 ± 0.3 years), and BMS was assessed via skeletal age using the BAUSport™ ultrasound device. When compared to players` expected BMS, a significant large pre-selection bias was observed favouring players with higher BMS to get selected for a regional association team (M = 15.1 ± 1.0, d = 1.19, p < .001). Positional analyses revealed significant differences in BMS (n2 = .14, p < .001) with goalkeepers, defenders, and forwards being biologically older than midfielders. Team performance (points achieved) showed a strong positive correlation with BMS (rs = .71, p < .001). Significant small advantages in maturity-related variables were found for players selected for the extended U15 youth national team squad (0.17 = d = 0.23; p < .05). Position-specific analysis of selection status revealed medium-to-large effects in forwards and goalkeepers with respect to BMS. The findings highlight the critical influence of BMS in multi-stage selection processes and underscore the need for position-specific considerations to ensure fair and developmentally appropriate talent promotion.
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