Differential response is one of three key areas targeted by California for improving child welfare services statewide. By applying the Breakthrough Series Collaborative (BSC) method to California’s implementation of differential response, the California Department of Social Services (CDSS) and its partners hoped to learn more about innovative practices that have the potential to improve outcomes for children and families. The BSC on differential response served as a successful laboratory for change. The practice changes that emerged provide a solid foundation for implementing and institutionalizing differential response in California. Full implementation of differential response is, of course, a long-term