Research indicates that participation in sport is associated with positive youth development (PYD), yet little is known about the mechanisms within sport that foster these positive outcomes. Existing measures of PYD in sport that are focused on outcomes, represent a mix of causal and outcome factors, and/or are missing potentially valuable experiences. Using the Sport-Based Model of Positive Youth Development (Holt et al., 2017) as a framework, this thesis sought to develop and test a measure of youth experience in sport. Three studies were conducted to achieve this objective. In Study One, N = 9 individuals (aged 13 to 38) participated in interviews about their experiences playing organized youth sports. Using findings from these interviews, literature, and expert review, a three-factor measure of youth experience in sport was developed to assess experiences of goal setting, adversity, and skill development. The factor structure of the Experience in Sport Scale for Youth (ESSY) was then evaluated using exploratory factor analysis in Study Two. With a sample of N = 334 adolescents (Mage = 17.36), a 19-item, three-factor model was retained. In Study Three, experience in sport, as assessed by the ESSY, was incorporated into the Sport-Based Model of PYD and tested as a mediating and a moderating factor in the association between PYD climate and PYD outcomes. A total of N = 453 undergraduate students (Mage = 18.46) completed measures of coach relationships, peer relationships, experiences in sport, and the 5 Cs of PYD. The overall model failed to converge. However, results indicated a significant association between goal setting and PYD outcomes of competence, confidence, character, caring, and connection. Furthermore, skill development was significantly associated with character and caring. Contrary to expectations, adversity was not significantly associated with any of the PYD outcomes. Implications for PYD research and future directions are discussed.