This 3-year longitudinal study investigated the associations of student (aged 9 to 10 years at the beginning of the study; n = 281; 51% girls) participation in extracurricular activities with teacher-rated socioemotional behavior and school achievement. MANOVA results showed that, after controlling for the grade level and the initial level of the outcome variables, participation in arts and crafts and music activities was related to higher adaptive behavior, academic attainments (i.e., reading, writing, arithmetic), and working skills (persistence, concentration, carefulness). Participation in performing arts was associated with higher academic working skills, and participation in academic clubs was related to higher academic attainments and lower levels of internalizing problems. Longer duration (2-to-3-years) of participation was generally associated with more positive outcomes. Sports activities were the most popular extracurricular activities, with individual sports more likely among girls and team sports among boys. (Contains 3 tables.)