This study described peer harassment in a large, multiethnic sample of adolescents, and explored the relationship between experiencing peer harassment and both school connectedness and achievement. Survey data came from 4,746 students in grades 7-12 at 31 public schools in ethnically and socioeconomically diverse communities in a Midwestern state. Frequency of five types of harassment were analyzed with data on school connectedness and grades. Multivariate analysis controlled for gender, grade level, race/ethnicity, and socioeconomic status. Results indicate that most students periodically experience mistreatment; 10% to 17% report being treated disrespectfully, having others act superior, or being insulted at least once per week, and an additional 14% to 22% of students report suffering these behaviors a few times per month. Girls, Whites, Native Americans, and middle school students reported more harassment than boys, other ethnic groups, and high school students, respectively. Peer harassment related significantly to both aspects of school life; those who disliked school tended to suffer more mistreatment, and "B" students reported the least harassment on average. Young people mistreated by peers may not want to be in school and may thereby miss out on the benefits of school connectedness as well as educational advancement. The high prevalence of peer harassment and its association with school connectedness and school achievement provide justification for interventions aimed at prevention of peer harassment. A schoolwide approach using educational and policy components may provide an appropriate prevention strategy.