This article examines the effect of classroom management strategies on students' interest development in secondary school mathematics classes. Two studies using student questionnaire data (one cross-sectional, with data from 400 students; the other longitudinal, with 1900 students) are reported. Results show that students' perceptions of rule clarity and teacher monitoring are positively related to their interest. Hierarchical linear modeling was used to examine the effect of classroom management on interest development over one school year, revealing that only individually perceived classroom management strategies and none of the class-level teaching characteristics (aggregated student data) affected interest development.