In the past five years, state education agencies (SEAs) have increased the number of social and emotional learning (SEL) policies, oftentimes engaging stakeholders across the state. However, few use multiple sources of stakeholder engagement data to develop and improve their SEL standards and resources (Yoder, Dusenbury, Martinez-Black, & Weissberg, 2020). This chapter describes the experience of a nonprofit research organization supporting an SEA and a volunteer workgroup in Washington state to gather and use several forms of stakeholder input and feedback in developing statewide SEL guidance for K-12 educators. Operating from a research-practice partnership framework (Coburn & Penuel, 2016), the team assisted the workgroup members in applying both an ecological systems theory perspective (Bronfenbrenner, 1979; Bronfenbrenner & Morris, 2006) and an equity lens to their work through an iterative process of data collection, interpretation, and use. This chapter describes the process and outcomes of this research-practice partnership and provides examples of how the workgroup incorporated stakeholder input and feedback into the development of SEL guidance and resources. We offer insights and lessons learned from these efforts to expand the perspectives represented in SEL research and policymaking. Our aim is to highlight the importance of stakeholder engagement to ensure that SEL guidance considers the priorities and values of diverse communities, especially historically marginalized communities. We hope to encourage more research-practice partnerships to investigate and amplify community perspectives in SEL. [For the complete volume, "Motivating the SEL Field Forward through Equity. Advances in Motivation and Achievement. Volume 21," see ED673001.]