The role of individual differences in second language (L2) learning is widely acknowledged; however, how teachers can accommodate individual differences in L2 classrooms receives relatively less attention. Focusing specifically on motivation, this study explores the effectiveness of communicative tasks on Korean L2 speakers' complexity, accuracy, fluency, and lexical dysfluency. Drawing upon the regulatory focus literature, the tasks were manipulated to emphasize either promotion or prevention motivational processes. Forty-seven participants were randomly assigned to either promotion or prevention task and completed a scale-based questionnaire to assess their overall orientation to instrumentality-promotion/prevention. For data analysis, learners were median-split into promotion and prevention groups based on their responses to the questionnaire items. 2×2 ANOVAs were conducted on linguistic measures to investigate the main and interaction effects of instrumentality-promotion/prevention and task-induced promotion/prevention on L2 task performance. The quantitative findings revealed that instrumentality-prevention had a negative effect on accuracy. However, task-induced promotion/prevention had no main or interaction effects on linguistic performance. Qualitative findings showed that the mismatch between instrumentality-promotion/prevention and task-induced promotion/prevention may distract attention from idea development during task performance. The findings are discussed in terms of pedagogical implications, in particular how to accommodate individual differences when developing teaching materials.