The education sector is embracing the hope that continuous improvement will lead to more beneficial student outcomes than standards-based reform and other approaches to policies and practice in prior decades. This report examines attempts in California to realize the potential of continuous improvement in some of the state's largest districts. Policy Analysis for California Education (PACE) and the "CORE Districts," a nonprofit collaborative of eight urban school districts, have been engaged in a research-practice partnership since 2015. This report presents lessons learned from their collaboration in 2018-19, and is accompanied by three case studies that provide a more in-depth discussion of exemplary practices in two districts and one school. The report opens by briefly defining continuous improvement and tracing the history of the "CORE Districts." It then focuses on two questions that are central if California's schools and districts are to realize the potential of continuous improvement. Six lessons gleaned through interviews, observations of professional learning events and team meetings, and analysis of artifacts created through learning events and improvement work are then described. The remainder of this report explains these lessons and implications for broader continuous work in California and beyond.