The objective of the paper is to report findings of two studies that attempted to find answers to the following questions: (1) What are the levels of cognitive engagement in TBL? (2) Are there differences between students who were more exposed to TBL than students who were less exposed to TBL? (3) To which extent does cognitive engagement fluctuate as a function of the different activities involved in TBL? And (4) How do cognitive engagement scores collected over time correlate with each other and with academic achievement? The studies were conducted with Year-1 and -2 medical students enrolled in a TBL curriculum (N = 175, 62 female). In both studies, six measurements of cognitive engagement were taken during the distinct TBL activities (preparation phase, individual/team readiness assurance test, burning questions, and application exercises). Data were analysed by means of one-way repeated-measures ANOVAs and path modelling. The results of the repeated-measures ANOVA revealed that cognitive engagement systematically fluctuated as a function of the distinct TBL activities. In addition, Year-1 students reported significantly higher levels of cognitive engagement compared to Year-2 students. Finally, cognitive engagement was a significant predictor of performance (β = .35). The studies presented in this paper are a first attempt to relate the different activities undertaken in TBL with the extent to which they arouse cognitive engagement with the task at hand. Implications of these findings for TBL are discussed.