This brief is one in a five-part series in which the Collaborative for Academic, Social, and Emotional Learning (CASEL) documents insights from their efforts to understand how educators and researchers can build relationships that support a shared action research agenda around social and emotional learning (SEL). As discussed in earlier briefs of this series (see ED614237 and ED614229), CASEL has continued to refine strategies and tools to better document the ways that technical assistance aids partner districts in advancing high-quality implementation of systemic SEL. Additionally, they have determined that a design-based Research-Practice Partnerships (RPP) approach affords opportunities to collaborate closely with administrators, practitioners, families, and students to develop a local SEL vision, monitor this work, and identify on an ongoing basis barriers and facilitators for achieving specified benchmarks and annual goals. CASEL's RPP engagement with Lowell Community School provided valuable insights into how CASEL research will approach collaboration with practitioners in the future. In addition to these insights, the engagement with Lowell Community School elevated new learnings related to systemic SEL implementation at the school level. CASEL's Theory of Action provides guidance to states, districts, and schools in their approach to systemic SEL implementation.