The present article focuses on in situ social comparison among junior high school students. Rather than studying social comparison as an individual phenomenon in experimental situations, which has been common in previous research, the study analyzes social comparison as a real-life social practice. The results show that the practice of social comparison among students reconnects to central elements of the formal assessment system. For instance, in staging comparison sequences, the students often circulated prior teacher assessments or engaged in various counting practices. Moreover, the results show that students partake in social comparison in order to establish, protect, or recapture an image as successful students. In so doing, they are socialized into a range of useful social-comparison practices. Despite this, some students necessarily turn out to be positioned lower than others. Thus, social comparison among students can be seen as an informal stratification process in the school system. (Contains 2 tables.)