Background: There is a growing body of research on situational interest (SI). Yet, we still know relatively little about how SI is supported in the classroom and the academic benefits of SI. Aim: The current study investigated (1) contextual antecedents of SI; (2) potential benefits of SI for academic outcomes; and (3) SI as a mediator of classroom practices to academic outcomes. Sample: Participants were 126 male and female adolescents (mean age = 14.6 years) who took part in a science course during a 3-week residential summer programme for talented adolescents. Method: Participants completed self-report measures prior to the start of the summer programme and at the end of the programme. Summer programme instructors completed ratings of students' engagement during the programme. Result: Multiple regression analyses were conducted to investigate the three study aims. After controlling for initial individual interest, perceived choice, instructor approachability, and course connections to real life were statistically significant predictors of SI during the summer programme, with varying associations observed based on the form of SI (triggered, maintained-feeling, and maintained-value). SI was positively related to individual interest and perceived competence in science at the end of the programme as well as teacher-rated engagement; SI also mediated the associations of classroom practices with these outcomes. Conclusion: Results suggest that classroom practices shape SI. In turn, SI supports motivation and engagement. Moreover, differentiated antecedents and outcomes of the three sub-components of SI were identified, highlighting the utility of this three-component approach for studying SI.