Despite the popularity of student engagement and, by association, student disengagement, the academic literature is unclear about the meaning of these terms. This review extends existing conceptual studies of student engagement by offering clear definitions and conceptualisations of both student engagement and disengagement in the classroom context. To develop these conceptualisations, the present review draws upon organisational behaviour theory on work engagement and disengagement because the literature in this discipline is notably more refined than in educational research. Using an organisational behaviour backdrop, student engagement and disengagement are defined by the degree of students' activation and pleasure. In order to operationalise student engagement, measures that are aligned with the proposed conceptualisation are recommended. Recommendations are also suggested for the development of a measure of student disengagement. The proposed measurement of student engagement and disengagement should provide a unified direction for future empirical research on these topics.