This paper examines the effect of teacher and peer characteristics on left-behind student outcomes. In this study, we exploit a nationally representative survey of middle school students in China and focus on schools that randomly assign students to classrooms. We find that: First, from the teacher aspect, female head-teacher and head-teacher’s credential status could improve left-behind students’ test scores. However, teacher’s prior experience and education level have no significant effects on left-behind students’ academic performance; Second, from peer aspect, a higher proportion of repeated children in class has negative effects on left-behind students’ performance. Third, teachers and peers’ characteristics can influence teachers’ teaching methods, engagement, and students’ learning motivation, which in turn affect the academic performance of left-behind children. Our study provides a multi-dimensional description on left-behind children’s educational achievements, and shed light on the debate concerning how to improve these children’s status.