This study investigated the relationship of students' sense of belonging in their classes to measures related to motivation, student effort, and academic achievement. Data from 612 fifth- through eighth-grade middle school students revealed that the sense of belonging in a class was related to: (1) students' expectations of academic success; (2) students' intrinsic interest in the schoolwork in the particular subject; (3) course grades; and (4) teacher ratings of students' effort. In general, the sense of belonging was most important among seventh graders, and was more important in low-consensus classes, such as social studies, than in high-consensus classes. Belonging is seen as situation-specific and as amenable to change through group processes in the classroom. A list of 32 references is included. (BC)