Why do some adolescents who participate in extracurricular sport benefit, whereas others do not? There is extensive research outlining the role sport plays in positive adolescent development (Barber, Abbott, Blomfield, & Eccles, 2009; Feldman & Majasko, 2005; Marsh & Kleitman, 2002). Despite this, findings also point to links between sport and risky behaviour, specifically alcohol use (Eccles & Barber, 1999; Modecki, Barber, & Eccles, 2014). To develop a more nuanced understanding of the sport context and explain this diversity of outcomes, this thesis examines individual differences among adolescent athletes and how these contribute to positive outcomes and risks among adolescents who are embedded in the sport environment. Thus, several approaches to the measurement of individual differences within the sport context are adopted to better understand how individual attributes of athletes may promote positive experiences within the sports context for some adolescents and contribute to susceptibility to risk for others. Data were collected for the three empirical studies from a sample of Western Australian adolescents in conjunction with the Youth Activity Participation Study of Western Australia (YAPS-WA. Study 1 (Chapter 3) utilizes Wave 4 data (Year 9 and year 12), study 2 (Chapter 4) uses longitudinal data from Wave 1 through to Wave 4 (Year 8 – Year 11). Study 3 (Chapter 5) also longitudinal, uses data from Wave 1 to Wave 3 (Year 8 – Year 10) (see Appendix A for a copy of the entire Wave 4 survey).