A total of 236 kindergarten to eighth grade students and 15 teachers from an elementary school in a northeastern U.S. city provided information about their perceptions of teacher involvement in students' peer relationships. Students provided additional information about classroom social networks. Both students and teachers indicated that they perceive teachers to be important in student peer relationships. None of the teacher characteristics (including teacher education, years of teaching, or ethnicity) were related to teacher perceptions of involvement in students' peer relationships. In lower grade groups (kindergarten to second grade), there were significant sex differences, with boys rating their teachers as more involved than girls; sex differences were not significant in either the middle (third to fifth grade) or upper (sixth to eighth grade) grade groups. As hypothesized, there were significant differences between grade groups, with students in the lower grades rating their teacher as more involved than students in either the middle or upper grade groups, and middle grade groups rating their teachers as more involved than the upper grade groups. Teacher and student perceptions of teacher involvement in students' peer relationships were then analyzed to determine whether these perceptions were related to classroom cohesiveness, as measured by social networks. The results were not significant, indicating that teacher and student perceptions of teacher involvement in students' peer relationships were not related to classroom social networks. This research provides a first look into both teacher and student perceptions into teacher involvement in classroom peer relationships, which school psychologists can use to help teachers construct supportive classroom environments. This research is a case study of one school, and therefore generalization from this sample is difficult. Future research should examine this element in schools of varying climate and region. / School Psychology