This chapter reports an empirical study examining the effects of pre-task planning and reasoning demand on Hong Kong ESL learners’ task engagement in face-to-face real-time communication contexts. Thirty undergraduate students worked in self-selected pairs to complete three interactive oral tasks with varying combinations of pre-task planning and reasoning demand. Learners’ spoken discourse was collected and analysed using discourse analytic methods to assess their behavioural, cognitive, and social engagement during task performance. Learners’ emotional engagement was captured through semi-structured interviews conducted immediately after each task. The findings indicate that participants were most behaviourally and emotionally engaged in the task that combined pre-task planning time with higher reasoning demand, while a range of emotions was expressed across all tasks. These results extend the Cognition Hypothesis to the domain of task engagement and underscore the importance of considering cognitive demand in the design of L2 oral tasks.