The article deals with the way in which authority was established and interpreted by teachers and students in two Flemish sixth-grade mathematics classrooms. Problem-solving lessons during a seven-month observation period were analysed regarding three aspects of teacher-student interactions that explicitly or implicitly reflect who bears mathematical authority: (1) to whom were students allowed to ask for help; (2) who was allowed to answer students' mathematics-related questions; and (3) who was allowed to evaluate students' responses. For each of these aspects, we were interested whether authority was ascribed only to the teacher or whether authority was distributed more broadly, with students being considered accountable for their own and other's learning process. Interviews with teachers and students were conducted to investigate the meaning that participants gave to the practices in which they were involved. (Contains 1 figure and 2 tables.)