We investigated and compared sociomathematical norms in secondary mathematics teachers' classrooms before and after using mathematical modeling activities. Participants were four secondary mathematics teachers. The data included 104 h of videotaped classroom observations and teacher interviews. The data analysis revealed notable changes in sociomathematical norms in teachers' lectures not utilizing modeling activities beyond those utilizing modeling activities. The results implied that teachers and students were convinced by and adopted what was done in the modeling environment. We discussed that modeling activities could be a powerful tool for mathematics teachers and students in challenging and transforming traditionally oriented classroom norms to those aligned with reform-oriented mathematical classrooms and their sustainability.