Student opposition in school is traditionally cast in terms of individual dispositions, whereby particular students or groups of students are said to “resist” or “oppose” school structures and identities aligned with the dominant cultural group. The author examined instead how the teacher and students in a low-track mathematics classroom jointly constructed opposition through their classroom interactions. Analysis of the classroom interaction revealed the emergence and escalation of a number of classroom practices that became oppositional. These practices were related to the nature of the mathematical activity, the framing and positioning of student participation in this activity, and multiple interpretations of student competence in and out of the classroom. The author found that classroom opposition is fostered by weak opportunities for meaningful mathematical engagement and the transformation of a polarized participation structure into an oppositional one.