This article presents results from an empirical study of how student engagement is visible during introductory algebra. Previously, the notion of engagement in mathematics has been studied from students' and researchers' perspectives. This study is instead focused on teachers' perspectives on student engagement. Eight teachers in grade 6-7 have shared video recorded episodes from their own lessons and a model based on those episodes is presented. The outcome of teachers' discussions shows that engagement is recognised as different types of student participation, indicated by specific student actions in the classroom. This study gives further insights into the notion of engagement as seen by teachers and provides specific examples, such as verbalising thinking, completing peer utterances and active listening.