This article answers a call for increased scientific precision in student engagement research by contributing a definition of engagement at the microlevel grain size of individual students’ momentary involvement in academic tasks. We build on the classroom engagement framework to create a conceptualization of momentary engagement as a dynamic system comprised of parts (emotion, motivation, mental action, and physical action) existing within an overarching structure (co-action between parts) that develops as a process (a sequence of engagement triggers, non-linear action and disengagement). This new conceptualization is discussed in relation to methods of studying momentary engagement focusing on the notions of complexity, emergence and dynamics. We conclude by calling for a paradigm shift in research on student engagement.