This explanatory sequential mixed methods study examined how belonging perceptions, academic motivation, and engagement might mediate the relationship between academic contextual characteristics and achievement using structural equation modeling and qualitative follow-up interviews with college students from a large, Midwestern university. In the first, quantitative phase, two hypothesized models of student belonging and motivation were tested. In line with the Self-System Model of Classroom Support for Motivation (Connell and Wellborn, in: Gunnar and Sroufe (eds.) Minnesota Symposium on Child Psychology: Self-processes and Development, 1991), Model 1 hypothesized student belonging and motivation to be directly predicted by supportive classroom environment perceptions, and to directly predict engagement, which was hypothesized to predict achievement. Model 2 elaborated on the traditional self-system model and hypothesized student belonging to mediate the relationship between supportive classroom environment perceptions and student motivation. Quantitative findings revealed support for Model 2. Supportive classroom environment perceptions predicted students' belonging beliefs, which in turn predicted students' motivation, engagement, and achievement in the course. The second, follow-up qualitative phase suggested ways in which contextual characteristics might influence student belonging beliefs in the classroom. Taken together, the quantitative and qualitative data illustrate the influential role of classroom contextual characteristics on student outcomes, as well as the role student belonging plays in college student motivation and success.