The quality of students' relationships with their teachers plays a significant role in their success in school. Social and emotional learning (SEL) curriculums show great promise for supporting student development. However, quality implementation requires that teachers recognize and understand how their behavior and interactions with students impact the development of these skills. The Prosocial Classroom Model proposes that teacher social and emotional competencies (SECs) play a critical role in creating and maintaining a classroom where everyone feels safe, connected, and engaged in learning. In this chapter, we extend the understanding of SEC to include leadership styles as defined by evolutionary motivational systems theory. We argue that a critical dimension of effective SEL instruction and teacher SEC is effective leadership that skillfully applies an understanding of the social and emotional dimensions of classroom interactions that promote motivation, engagement, and learning. Implications for educational theory, policy and practice, and research are discussed. [For the complete volume, "Motivating the SEL Field Forward through Equity. Advances in Motivation and Achievement. Volume 21," see ED673001.]