Relative age describes the age differences within age groups in sport and education. Relative Age Effects (RAE) indicate that being older within an age group cohort typically results in advantages in sport and academic outcomes (Musch & Grondin, 2001). However, previous research has predominantly isolated relative age's influence on development outcomes (i.e., sport participation or academic achievement). This study explored interactions between relative age, educational achievement, participation in school and extracurricular sport, and an indicator of positive youth development (i.e., feelings of connectedness to school). A secondary analyses of Ontario secondary school students (N = 22,915; average age = 15.7, SD = 1.25; 50.2% female) from the COMPASS study was conducted. Overall, the greatest percentage of students who participated in sports was found in Quartile 1, followed by Quartiles 2, 3 and 4 (x2 range = 20.12 - 60.91, p < .001). There was also a statistically significant effect of relative age (favouring relatively older youth) on feelings of connectedness [F(3, 21978) = 5.50, p = 0.001]. Moreover, sport participation was positively related to academic achievement and feelings of connectedness (OR = 1.15). Finally, feelings of connectedness were positively related to sport participation as well as higher academic achievement, for all relative age quartiles. Future research should seek to investigate the effects of relative age on other youth sport and education outcomes, especially as they relate to positive youth development and other multi-dimensional aspects of youths' developmental ecology (e.g., socioeconomic status and participation in other non-sport extracurricular activities).