California and the nation are at the crossroads of a major shift in school accountability policy. At the state level, California's Local Control and Accountability Plan (LCAP) encourages the use of multiple measures of school performance used locally to support continuous improvement and strategic resource allocation. Similarly, the federal Every Student Succeeds Act (ESSA) reinforces this local control, requiring more comprehensive assessment of school performance and a less prescriptive, local approach to school support. These changes represent a major cultural shift for California schools and districts. Ahead of the curve, six California districts, known as the California Office to Reform Education (CORE) waiver districts, have implemented an innovative measurement system and supports for school and district improvement under an NCLB waiver, and thus provide a unique opportunity to examine and learn from the enactment of a system supported by accountability policy in this new era. This report examines the early implementation and effects of the CORE reform and seeks to inform the ongoing efforts within CORE as well as the development and implementation of future accountability policy in other states and districts. Additional details about the research methods are appended. [For the accompanying policy brief, "Local Control in Action: Learning from the CORE Districts' Focus on Measurement, Capacity Building, and Shared Accountability. CORE-PACE Research Partnership. Policy Brief 16-4," see ED574788.]