It can be challenging for teachers to engage students online; to know whether students are engaged or not. Online engagement can be perceived differently than in-class engagement. Research has shown that teacher perceptions of student engagement affect how they interact with students as well as students’ grades. It is critical to understand how teachers perceive engagement, not least in an online setting, to inform practices and research. This study explores Swedish teachers’ understanding of student online engagement and disengagement. A Mixed Method Grounded Theory study was designed as an intervention with an interview-diary-interview format. Twenty interviews with teachers (n = 10) who regularly teach hybrid, remote or distance classes in K-12 education were analysed using descriptive statistics and content analysis. The results show that teachers express understanding at the macro and micro level of engagement and would report different combinations of engagement and disengagement at different levels of engagement. The results informed an engagement model with a complex construct without inherent boundaries; teachers rated student engagement both below and above the suggested scale. The contribution to theory with included models is discussed. © 2022 The Author