Evidence that childhood maltreatment is associated with emotional and behavioral problems throughout childhood suggests that maltreatment could lead to impaired academic performance in middle and high school. This article explores these effects using data on siblings. An index measure of the intensity of childhood maltreatment was included as a covariate in multivariate analyses of adolescents' risk for school performance impairments. Family fixed effects were used to control for unobservables linked to family background and neighborhood effects. More intense childhood maltreatment was associated with greater probability of having a low grade point average (P=0.001) and problems completing homework assignments (P=0.007). Associations between maltreatment intensity and adolescent school performance were not sensitive to model specification. Additional analyses suggested that maltreatment effects are moderated by cognitive deficits related to attention problems. The implications of these findings for educators and schools are discussed.