Peer harassment is a major social problem affecting children and adolescents internationally. Much research has focused on student-to-student harassment from either an individual or a multilevel perspective. There is a paucity of multilevel research on students' relationships with the classroom teacher. The purpose of this study was to use a socioecological perspective to examine the relationships between individual student-level characteristics, problematic teacher-student relationships, and student-reported peer harassment. A total of 1,864 children (50.7% female) aged 8 to 13 years (M = 9.82, SD = 1.24), nested in 27 schools (58.2% public) in Spain, participated in the study. Ninety-four homeroom teachers reported on teacher-student relationships, and students completed self-report measures related to peer harassment and teacher-student relationships. Multilevel models showed that relationships between students and teachers exerted a varying degree of influence on classroom levels of peer harassment. Specifically, student-reported teacher support was associated with diminished student-reported peer victimization, whereas direct and indirect student-reported teacher-to-student aggression was associated with increased peer victimization. Additionally, student-reported student-to-teacher aggression and teacher-to-student aggression were associated with increased student-reported peer aggression. Teacher-reported variables at the classroom level, however, contributed little to student-reported outcomes. Results are discussed in the context of future research on relationships between teachers and students.