Each year, between 10 and 20 percent of schoolchildren in the United States are exposed to domestic violence. According to psychologists, such exposure can lead to aggressive behavior, decreased social competence, and diminished academic performance. A majority of parents and school officials believe that children who are troubled, whatever the cause, not only demonstrate poor academic performance and inappropriate behavior in school, but also adversely affect the learning opportunities for other children in the classroom. Understanding whether troubled children in fact generate spillover effects in school is important for two reasons. First, the existence of substantial spillovers caused by family problems such as domestic violence would provide an additional compelling reason for policymakers to find ways to help troubled families. Second, because many education policies change the composition of school and classroom peer groups, it is important to understand how such changes may affect student achievement. In this study, the authors utilize a unique data set in which information on students' academic achievement and behavior is linked to domestic violence cases filed by their parents. This data set allows them to identify troubled children more precisely than they could by using conventional demographic measures. Moreover, they can identify children who are troubled for specific family reasons and not because of their peer group. This allows them to measure peer effects free from the reflection problem, providing a rare opportunity to test the notion that even one "bad apple" impedes the learning of all other students. The results confirm, first, that children from troubled families, as measured by family domestic violence, perform considerably worse on standardized reading and mathematics tests and are much more likely to commit disciplinary infractions and be suspended than other students. The authors find also that an increase in the number of children from troubled families reduces peer student math and reading test scores and increases peer disciplinary infractions and suspensions. The effects on academic achievement are greatest for students from higher income families, while the effects on behavior are more pronounced on students who are less well-off. The results of the authors' analysis provide evidence that, in many cases, a single disruptive student can indeed influence the academic progress made by an entire classroom of students. (Contains 2 figures.)