The combination of changes occurring at the transition to middle school may be a catalyst for the onset of depressive symptoms, yet teacher support at this transition is protective. Research points to certain temperamental traits as risk factors for developing depressive symptoms. This study examines student reports of teacher support and teacher reports of student-teacher relationship (STR) quality as mediators of associations between child temperament (i.e. negative emotionality at age 4½ and emotional reactivity in elementary grades) and depressive symptoms in sixth grade. Results indicate (a) negative emotionality predicted emotional reactivity and depressive symptoms; (b) emotional reactivity predicted depressive symptoms; (c) students' perceptions of teacher support (in grade 6) and teachers' perceptions of STR quality (in grades 4-6) predicted depressive symptoms; and (d) student-teacher conflict mediated associations between emotional reactivity and depressive symptoms. Findings point to the importance of teacher support and positive STRs during the transition to middle school.