This study aimed to identify organized sports participation patterns and their prevalence from adolescence to emerging adulthood, and the educational and family-related determinants of the patterns. Adolescents in the Finnish Health Promoting Sports Club (FHPSC) study answered a health behaviour questionnaire and reported on sports club participation at ages 15 and 19 (N = 609). In emerging adulthood, dropouts (total 41.05%; females 43.72%; males 36.56%), maintainers (30.87; 26.44; 38.33), nonparticipants (27.59; 29.32; 24.67), and joiners (0.49; 0.52; 0.44) (p = .024) were identified. A mixed multinomial logistic regression analysis showed, that male gender, as compared to female gender, increased the odds of being a maintainer rather than a nonparticipant or dropout. Among females, high achievement at school and aspiration towards upper secondary school at age 15 increased the odds of being a maintainer at age 19 rather than a nonparticipant. High achievement at school and experiencing a (strong) decrease in parental support for physical activity/sport increased the odds of being a dropout rather than a nonparticipant. Having no experience of a strong decrease in parental support increased the odds of being a maintainer rather than a dropout. Among males, aspiration towards upper secondary school increased the odds of being a maintainer or dropout rather than a nonparticipant. The most common reason for dropping out was study, which was also the most prevalent life status at age 19. The findings highlight a need for more flexible possibilities to combine organized sports participation and school studies, and the importance of parental support for physical activity/sport.