This practitioner brief is the first in a series highlighting concrete strategies that educational leaders can use to increase equity in education, by building supportive learning environments that meet all students' social and emotional needs. This introductory brief starts by laying out the aspects of a student's social and emotional well-being that are the most strongly related to school engagement. It then describes how environmental and structural factors facing particular groups of students lead to disparities in these aspects of social and emotional well-being that affect learning. The discussion then turns to three levels of change that are needed to address this inequity: making equity-focused structural and policy changes, enhancing staff capabilities, and enriching the social and emotional support available to students. Subsequent briefs will flesh out specific relevant issues, providing evidence for various strategies and implementation advice from educators who are using them. How a particular district proceeds will depend on its circumstance and resources, but this brief and future ones should help educators striving to make their systems more equitable.