Background: Prior research has shown that engagement plays a significant role in students' academic learning. Aims: The present study sought to expand the current understanding of students' engagement by examining how situational engagement during a particular lesson is associated with the observed teacher-student classroom interactions (i.e., emotional support, instructional support, and classroom organization) in the same lesson. Sample: The participants were 709 Grade 7 students (47.7% girls) from 59 classrooms in 26 lower secondary schools and 51 teachers. Methods: The data consisted of 155 video-recorded lessons (90 language arts and 65 mathematics lessons) coded using the Classroom Assessment Scoring System -- Secondary (CLASS-S) observational instrument. Students' self-ratings of their situation-specific engagement were collected using the mobile-based In Situations (InSitu) Instrument at the end of each lesson. The data were analyzed with cross-classified two-level hierarchical modelling. Results and conclusions: The results indicated that emotional support in the classroom was positively associated with students' emotional engagement and help-seeking, whereas classroom organization was associated with students' behavioural and cognitive engagement. Overall, the findings provide novel evidence suggesting that students' engagement can be fostered by supportive teacher-student interactions.