This article examines the literature on student engagement in the classroom or school in order to suggest a socio-culturally inspired definition of this construct, one that emphasizes participation in context rather than defining it along three or four dimensions. Six nuclei of activities are distinguished, three at the micro level and three at the macro level: 1) Attention to the teacher's discourse; 2) Direct interaction with the learning object; 3) Interaction with peers to carry out a project, understand the meaning of a question or a problem, explore it further, or even solve it in a learning or knowledge-building community; 4) School attendance; 5) Expected or constructive contribution to the dynamics of a group; 6) Contribution to the environment, to a local or external community. To illustrate these, the PERISCOPE network’s repertory of publications was searched, and 61 publications were selected according to independent criteria. Although the manifestations of student engagement are likely to multiply and diversify, the six activity nuclei have thus passed a first validation test.