This classroom-based exploratory study examined the relationships between affective, social, and cognitive aspects of second language (L2) learners' task-based performance. In responding to practical challenges when TBLT is implemented in the real-world context, we collected observational data from multiple sources. In the study, 96 high-school EFL learners in Chile formed 32 groups and completed a decision-making task. The affective aspect was operationalized as interaction mindset and engagement, while the social aspect was gauged by group work dynamics, including verbal and non-verbal data. The cognitive aspect pertained to L2 use (the number of words, turns, and language-related episodes). The data included (a) video-recorded group work, (b) the interaction mindset inventory, (c) the idiodynamic measure targeting engagement, and (d) retrospective interviews. The network analysis revealed that the social aspects exerted the most influential role, which was best represented by turn-taking behaviors. The microanalysis of two groups showed that in unpredictable moments, learner engagement converged among the group members-group synchronicity-at which point learners took turns smoothly and resolved language-related issues collaboratively. We conclude that what learners do with the task in the classroom may provide more pedagogically informative evidence than what the internal structure of the task might do to learners.