Objective. To investigate the longitudinal associations of moderate-to-vigorous physical activity (MVPA) and pubertal development with academic achievement in adolescents.

Methods. A total of 635 adolescents (283 boys, 352 girls) aged 11–13 years participated in the study. MVPA was assessed by the Health Behaviour in School-aged Children study questionnaire, and pubertal development was assessed by the pubertal development scale (PDS) at beginning of 6th grade (baseline) and end of 7th grade (follow-up). Grade point average (GPA) at the end of Grades 5 and 7 was computed from data acquired from the school registers. The data were analysed using linear regression and analyses of covariance.

Results. In boys, MVPA was positively associated with GPA at baseline after adjustment for age (β = 0.144, 95%CI: 0.028−0.260, p = 0.028). In girls, PDS was positively associated with GPA at baseline (β = 0.104, 95%CI: -0.004−0.211, p = 0.058) and follow-up (β = 0.104, 95%CI: -0.002−0.211, p = 0.055) after adjustment for age, and these associations strengthened after further adjustment for MVPA (p < 0.05). Adolescents who were inactive at baseline or at baseline and follow-up had lower GPA during follow-up than their continuously highly active peers (mean difference = -0.301, 95%CI: -0.543 to -0.058, p = 0.009) and all other adolescents (mean difference = -0.247, 95%CI: -0.475 to -0.019, p = 0.029). These differences were greater in girls than in boys.

Conclusion. Lower levels of MVPA were associated with lower GPA in boys at baseline. Girls who were continuously inactive had lower GPA over the follow-up period than those who were continuously active. Finally, earlier pubertal development was associated with better academic achievement in girls.