This study investigated associations among third-grade teachers' (N = 27) symptoms of depression, quality of the classroom-learning environment (CLE), and students' (N = 523, Mage  = 8.6 years) math and literacy performance. teachers' depressive symptoms in the winter negatively predicted students' spring mathematics achievement. This depended on students' fall mathematics scores; students who began the year with weaker math skills and were in classrooms where teachers reported more depressive symptoms achieved smaller gains than did peers whose teachers reported fewer symptoms. teachers' depressive symptoms were negatively associated with quality of CLE, and quality of CLE mediated the association between depressive symptoms and student achievement. The findings point to the importance of teachers' mental health, with implications for policy and practice.