This study examined profiles of participation in extracurricular activities (ECAs) in 4th grade children (N = 27,121; Mean age = 9.20 years; SD = .54; 51% male) in British Columbia, Canada. Latent class analyses were used to establish activity profiles and determine class membership; ANCOVA was used to investigate differences in mental wellbeing (optimism, life satisfaction, self-concept) and perceived overall health between groups. Data came from a cross-sectional, population-level child self-report survey (i.e., the Middle Years Development Instrument) implemented with 4th grade children in public schools. We found four distinct ECA profiles: participation in "All Activities", "No activities", "Sports" (i.e., individual and team sports), and "Individual activities" (i.e., educational programs, arts/music, individual sports). Wellbeing and health scores were highest for children in the "All Activities" and the "Sports" clusters, and lowest for those in "No Activities" and the cluster reflecting individual activities (i.e., "Individual activities"). Results are discussed in the context of previous research, and with respect to practical relevance.