In 2012, California was awarded a competitive four-year federal Race to the Top-Early Learning Challenge (RTT-ELC) grant to develop a locally administered, state-supported Quality Rating and Improvement System (QRIS). The California Department of Education has co-led a state implementation team with First 5 California to support county-based Consortia in developing and implementing the state's QRIS rating criteria. In January 2013, 17 Consortia initiated a QRIS that would expand and strengthen preexisting quality improvement initiatives in 16 counties. The RTT-ELC grant requires an independent evaluation and validation of the QRIS to determine whether ratings are actually associated with higher program quality and whether they can be used to predict children's developmental gains. To this end, the state contracted with American Institutes for Research (AIR) and its partners at RAND Corporation to conduct this study in 2014 and 2015. The study team collected data in a sample of fully rated sites, including independent observations of classroom quality, a survey of providers about their participation in quality improvement activities, and direct assessments of developmental outcomes of 3- and 4-year-old children. However, given the relatively short funding time frame, the mandated evaluation had to begin before the QRISs were fully implemented. Consequently, the key takeaway messages presented below must be considered tentative and mainly should be used to guide refinement of the system and inform the next stage of evaluation. (author abstract)