Background: Theory, methods, and knowledge gained from years of study in psychological science and human development apply to the understanding and improvement of teacher quality and, ultimately, student achievement and social and emotional outcomes. With these applications, educational research has stronger potential to make more effective and systematic contributions to the improvement of teaching in American schools. This potential can be realized by linking the scientific study of psychology and teachers' development (social, relational, psychological, and cognitive) to teachers' classroom behaviors (the mechanisms and processes underlying quality) and student achievement of educational and social and emotional objectives (the outputs of quality). New funds of knowledge in developmental and psychological science can serve as a basis for future research on inputs into teacher quality. Purpose: The present article advances an interdisciplinary perspective on the factors influencing teacher quality, specifically defined as teachers' practices and their interactions with students that can be shown to relate to student achievement. The article (1) offers a view of teacher quality focused on teacher-child interactions that serve as explanatory mechanisms in predicting children's achievement; (2) introduces key principles of human adult development that offer insights to link developmental research on teachers to teacher quality and, ultimately, to student achievement and social and emotional outcomes; and (3) discusses two bodies of research from psychological science that illustrate the ways in which psychological principles and an overarching view of teachers as developing people may contribute to current debates about teacher quality. Research Design: The article synthesizes research from the fields of education and psychology. Conclusions: The article closes with recommendations for basic, developmentally oriented research on teacher quality and student achievement.