This three-wave longitudinal study aimed to investigate whether the relationship between self-control and academic achievement, through mastery goals, was conditional on the nature of the teacher-student relationships. A total of 852 junior school students in China completed questionnaires about self-control, mastery goals, and teacher-student relationships. Academic achievement was obtained from the school. The analyses of moderated mediation effects based on structural equation modeling showed that teacher-student emotional conflict increased the negative effect of students' low self-control on academic achievement via mastery goals, whereas teacher-student emotional support failed to moderate this link. Thus, both mediating and moderating effects exist in the association between self-control and adolescents' academic achievement.