This study aimed to test a model of classroom social climate, growth language mindset, boredom, and student engagement among English as a foreign language (EFL) learners. In addition, the mediating role of boredom in this structural model was examined. To this end, 287 English major students from various universities in Iran participated in the study by completing valid measures of the four constructs under investigation. The construct validity of the measures was verified through confirmatory factor analysis (CFA). Moreover, structural equation modelling (SEM) was conducted in order to demonstrate an adequate fit to the data in the study. SEM results demonstrated that classroom social climate and boredom significantly predicated EFL student engagement directly. However, the growth language mindset affected student engagement indirectly, through the mediating effect of boredom. The results might offer a point of departure for future studies and also have significant implications for both EFL learners and instructors.