Declining motivation in mathematics among students remains an educational concern. This study examined the mediating effects of autonomous learning and competence on the relationship between the teacher–student relationship and mathematics motivation, using a predictive research design with mediation analysis and a survey of 187 junior high school students selected through stratified random sampling. Results showed that the autonomous learning variable did not mediate the relationship, while the competence variable did. These findings partially support Self-Determination Theory. Future research may explore other motivational variables that influence students' motivation in mathematics.