The goal of our article is to consider the intersection of the peer ecology and teacher practices for students' academic motivation. We begin by reviewing two perspectives that explain why and how peers matter for students' motivation. First, the quality of peer relationships and interactions provide affordances for "social support." Second, peers are "socializing" agents, so the content of peer interactions matters for the development of students' achievement beliefs, values, and goals. Within each of these theoretical frameworks, we discuss three kinds of peer relationships: friendship, social status, as well as the culture of support and norms that characterize the classroom peer group. Throughout, we consider classroom contextual factors that explain why peer relationships matter for students' motivation and school adjustment. This sets the stage for the key goal of our article, which is to review evidence from the last ten years linking teacher practices to aspects of the classroom peer ecology that are important for students' motivation in school. We conclude with a discussion of implications for educators and important directions for future research.