California became the nation's second state to approve charter schools when it passed legislation in 1992, and it currently has more charter schools than any other state. Developed during a post-civil rights era, charter schools are not attached to civil rights policies. This study is based on the integration theory of choice and uses an explanatory sequential mixed methods design to explore racial, socioeconomic, and linguistic segregation in California's charter schools compared to traditional public schools (TPSs), and in some cases, magnet schools, and the ways in which charter policies and practices relate to level of segregation. Segregation trends are analyzed for the state, Riverside Core Based Statistical Area (CBSA), Sacramento CBSA, and Los Angeles Unified School District using measures of concentration and exposure/isolation. The relationship between segregation and academic achievement in charter schools compared to TPSs is analyzed using ordinary least squares regression. Interviews with leaders, teachers, and parents at three charter schools in Los Angeles are analyzed to identify mechanisms related to varying levels of segregation.

Findings indicate that segregation is intensifying in California's charters and TPSs. While the disparities in enrollment and segregation between charters and TPSs are generally modest, charters tend to enroll disproportionately large shares of advantaged students and small shares of historically disadvantaged students. Charters tend to be more segregated than TPSs. High levels of segregation are correlated with lower academic achievement in both charters and TPSs. The relationship between segregation and academic achievement in charters compared to TPSs varies among geographic areas, but generally in segregated schools, charters outperform TPSs, and in desegregated schools, TPSs outperform charters. Three categories of school-level mechanisms are related to segregation: 1. founding decisions about the mission, type, location, and facility; 2. policies and practices around outreach, recruitment, enrollment, transportation, curriculum and instruction, student support services, and teacher diversity; and 3. responses to families' attitudes toward diversity and approaches to information sharing. District and state policies also influence these mechanisms.

The findings generate implications for policy and practice in multiple areas, including diversity goals, siting decisions, transportation, facilities, information dissemination, enrollment, curriculum and instruction, teacher hiring, and housing.