Teacher motivation and learner engagement are two essential elements of effective teaching and learning. However, while much research has examined them separately, fewer studies have explored how they interact over time in classroom settings. This paper investigates the reciprocal relationship between teachers’ motivation and students’ engagement in language classrooms. Drawing on a longitudinal mixed-method study, the research aims to understand how teachers’ motivation changes during the academic year, how it influences students’ participation and how student engagement feeds back into teachers’ professional identity and commitment. The study also connects these classroom dynamics to institutional priorities and educational policy contexts. Findings are expected to highlight how teachers and learners mutually shape each other’s motivation, offering insights for teacher education, school leadership and policy development.