"Making Assessment Work: Ten Practitioner Beliefs" was developed by the National Practitioner Advisory Group on Using Data to Inspire SEL Practice (NPAG), a group of social and emotional learning (SEL) practice leaders convened to provide insights on SEL. Educators, program leaders, and policymakers recognize the value of holistically supporting young people's social, emotional, and academic development. Assessment of social and emotional competencies helps paint a fuller picture of youth's capabilities and needs. As widespread implementation of SEL practices gains traction, SEL data are increasingly available in multiple forms. Key to the effective assessment of social and emotional competencies, the authors believe, is a continuous improvement lens: that is, the understanding that SEL data can be used in conjunction with other data to improve efforts, rather than evaluate or categorize youth and adults. Those who intend to measure and assess SEL must guard against bias, assess for sound reasons, protect individual privacy, and consider the strengths of youth and adults. This consensus statement reflects NPAG's insights on how assessment of social and emotional competencies, as well as SEL practices, should be planned, implemented, and interpreted. This document is the culmination of the authors' efforts, as well as a basis for new conversations about exactly how, why, and to what end SEL assessment should occur. The hope is that this position statement guides future actions about assessing SEL ethically and from a strengths-based perspective. The authors hope that the 10 beliefs, summarized in this article, can serve as a springboard for additional discussion, collaboration, and advancement of the work by researchers and practitioners alike.