The goal of this primer is to help education leaders understand the mutually reinforcing relationship between social and emotional development and ambitious academic goals. Instruction that promotes students' social and emotional development (SED) facilitates better student outcomes on college- and career-ready (CCR) standards. The converse is also true: Learning environments structured to genuinely meet rigorous standards support the development of students' social and emotional skills. To promote deeper learning, educators need to make the most of this interconnected relationship, and to approach SED not as an add-on or discrete intervention, but as an integral part of the academic program. This primer presents an approach to defining SED, which connects the overlapping terms that educators, developmental psychologists, neuroscientists, and economists use to describe these skills, and provides a summary of the research demonstrating the positive impact of SED. It highlights the required SED skills for a selection of English, mathematics, and science standards, drawn from several different states and organizations to illustrate how CCR expectations from across the country are dependent on SED. To provide additional guidance, the primer closes with a set of a reflective questions and considerations to support system leaders, principals, and teachers who pursue this work.