Student engagement is a strong predictor of academic achievement and overall school success. Much of the research on engagement has focused on the role of personal psychological antecedents and social factors related to one’s teachers. Relatively fewer studies have focused on the influence of one’s classmates. Drawing on prior work on social contagion, this study aimed to examine whether classmates’ engagement influences one’s engagement. Questionnaires were administered to 848 secondary school students nested within 30 classes. Two waves of data were collected seven months apart. Multilevel modelling showed that a student’s Time 2 engagement was positively predicted by his/her classmates’ engagement at Time 1, providing evidence for the social contagion of engagement. These findings held even after controlling for autoregressor effects and other relevant covariates such as demographic factors and achievement goals. Our results suggest that students’ engagement in school is contagious and could be transmitted among classmates.