Background: Much work has focused on "inattention" in the classroom, examining how episodes of task-unrelated thought (i.e., mind wandering) and engagement with various forms of media (e.g., media multitasking, smartphone use) influence retention of lecture material. However, considerably less work has examined factors that may positively influence attentiveness in lectures. Aims: We aimed to explore whether the trait-level tendency to experience 'flow'--defined here as the subjective experience of deep and effortless concentration--is related to in-class reports of engagement and understanding during undergraduate lectures, as well as academic performance. Sample: Participants were undergraduate students in Psychology at a University in Ontario, Canada. Methods: We measured trait flow (i.e., deep, effortless concentration) at the beginning of each semester, and assessed engagement and understanding during lectures via experience sampling probes throughout two semesters in several university courses. Experience sampling probes were presented intermittently using a laptop application. We also measured students' trait mind wandering and grit, and collected students' course grades. Results: The general tendency to experience deep, effortless concentration predicted engagement and understanding in lectures throughout the term, as well as final course grades, over and above students' grittiness and tendency to mind wander. Conclusions: These findings suggest that the everyday tendency to experience flow extends to a classroom environment and has implications for academic success.