The present study investigates the effects of participation in academic extracurricular activities on student achievement in mathematics and reading in the course of secondary schooling. We use 2 samples of nonmandatory all-day schools that are part of the National Educational Panel Study (NEPS): N = 1,131 fifth graders at 43 schools were followed until Grade 7 and N = 1,545 seventh graders at 64 schools until Grade 9. We compare students participating in all-day schools' extracurricular activities homework support, remedial education, and subject-specific programs to nonparticipating students. After controlling for prior achievement and further student background variables as well as estimating school fixed effects, we find no effects of participation in extracurricular activities on student achievement for both samples and both outcomes. The study contributes to the evidence base on the effects of extracurricular activities. We discuss the findings in light of the international discourse on effective extracurricular activities.