The authors explored how classroom gender composition moderated the relationship between having classmates with emotional and behavioral disorders (EBD) and peers' academic achievement in both kindergarten and Grade 1 classrooms. Given the behavioral and social-cognitive styles of girls, it was hypothesized that classrooms with a higher percentage of girls would moderate (or reduce) the academic consequences associated with exposure to children with EBD. To address this hypothesis, this study relied on applying quasi-experimental methods to a nationally representative data set (i.e., Early Childhood Longitudinal Study-Kindergarten Class) of U.S. elementary school students. Consistent with prior research, the findings revealed that exposure to a classmate with EBD resulted in lower reading and mathematics scores for classmates. However, classrooms with a higher percentage of girls were found to protect other students' academic achievement when in the presence of an EBD classmate. The findings presented in this study can be used to challenge educators and policy makers to develop support classroom environments for all students. Educational implications are discussed.