Given the importance of student engagement for students' current and future success, it is essential to explore how teachers can foster student engagement within lessons. This study relied on classroom observations to describe how teachers applied Self-Determination Theory (SDT) related (de)motivating teaching behaviours to foster students' engagement. Results from 120 observed lessons of 43 teachers indicated there were distinct relations between motivating teaching behaviours and student engagement. Most striking regarding the use of motivating teaching behaviours were the higher levels of relatedness support and guidance during activities in lessons in which students showed the highest levels of engagement. Conversely, in lessons where students were least engaged, teachers showed higher levels of chaotic teaching behaviours. Analyses of behaviours within lowly and highly engaging lessons showed that teachers in highly engaging lessons were observed to start with high levels of enthusiasm and after about ten to fifteen minutes focused on activating their students by offering room for experimenting and support while students worked on assignments. In contrast, teachers in lowly engaging lessons seemed to have a tendency to employ demotivating teaching behaviour at the start of the lesson. Implications and directions for future research are discussed.