Background: Students' self-concept of ability is an important predictor of their achievement emotions. However, little is known about how learning environments affect these interrelations. Aims: Referring to Pekrun's control-value theory, this study investigated whether teacher-reported teaching quality at the classroom level would moderate the relation between student-level mathematics self-concept at the beginning of the school year and students' achievement emotions at the middle of the school year. Sample: Data of 807 ninth and tenth graders (53.4% girls) and their mathematics teachers (58.1% male) were analysed. Method: Students and teachers completed questionnaires at the beginning of the school year and at the middle of the school year. Multi-level modelling and cross-level interaction analyses were used to examine the longitudinal relations between self-concept, teacher-perceived teaching quality, and achievement emotions as well as potential interaction effects. Results: Mathematics self-concept significantly and positively related to enjoyment in mathematics and negatively related to anxiety. Teacher-reported structuredness decreased students' anxiety. Mathematics self-concept only had a significant and positive effect on students' enjoyment at high levels of teacher-reported cognitive activation and at high levels of structuredness. Conclusions: High teaching quality can be seen as a resource that strengthens the positive relations between academic self-concept and positive achievement emotions.