Background/Context: The 1954 U.S. Supreme Court decision on Brown v. Board of Education concluded that segregated schools were inherently unequal and therefore unlawful. That decision was not based solely upon the notion that segregated black schools were inferior in terms of academic instruction, curricular rigor, resources, etc., but also on research that showed segregating black children had negative social-emotional and behavioral consequences. However, the vast majority of the research on school segregation over the past 50 years, has focused on its effects on academic achievement and opportunity to learn. As a result, little is known about the effects of school segregation on social-emotional and behavioral outcomes. This is a critical gap in the literature because other research indicates that school behaviors are as strong or stronger predictors of long-term educational, social, and employment outcomes as academic achievement. Objectives: The purpose of this study is to examine the effects of three forms of school segregation--socioeconomic, ethnic/racial, and linguistic--on school behaviors (i.e., attendance, grade retention, and suspension) and academic performance (reading and math achievement test scores and GPA) in high school. The study also examines the degree to which each of three school mechanisms (school inputs, peer influences, and school practices) mediates the effects of segregation on student outcomes. Research Design: The study uses survey data from the Educational Longitudinal Study of 2002 (ELS:02). A sequence of multilevel models are fit to the data to address the research objectives. Conclusions: American high schools are highly segregated by race/ethnicity, socioeconomic status, and English language status. Racial/ethnic and socioeconomic segregation are strongly associated with school behaviors and academic performance. The negative effects of racial/ethnic and socioeconomic segregation on school behaviors and academic performance inordinately effect black, Hispanic, and low SES adolescents because they are far more likely to attend segregated schools. School practices that reduce disorder and disruption and emphasize academics strongly mediate of the effects of segregation as does having friends at school with an academic focus. Adopting positive behavioral practices to reduce behaviors that interfere with learning without increasing suspension and expulsion are likely most critical for ameliorating the effects of segregation. Reducing academic tracking is also recommended, given that it likely contributes to negative within-school peer influences among low SES and minority adolescents. However, greater integration is likely necessary to fully address the consequences of segregation.