This study examines the antecedents and outcomes of classroom engagement of 412 Turkish English as a Foreign Language (EFL) learners. Grounded in self-determination theory and the self-system model of motivation, this mixed-methods study examined the relations between context (perceived autonomy-support from the instructor), self (basic psychological needs), action (behavioral, emotional, agentic, and cognitive engagement), and outcome (achievement and absenteeism). The results of structural equation modeling supported the hypothesized model and showed that learners’ perception of their teachers’ autonomy-support within the classroom predicted their need satisfaction, which in turn predicted self-determined engagement. Engagement predicted achievement and absenteeism within English courses. Semi-structured interviews showed patterns consistent with the quantitative results, and also that students felt their engagement would best be supported in classes with a positive social atmosphere. As well, their comments underscored the important role of language teachers in supporting learners’ psychological need satisfaction, classroom engagement, and positive academic outcomes. The findings suggest strategies for English language educators to bolster students’ engagement within the classrooms, including students who seem to be unmotivated, reluctant language learners.