Motivated by cognitive-interactionist frameworks for task-based learning, this study explored whether task complexity affects the extent to which learners focus on form-meaning connections during task-based work in a classroom setting, and whether this relationship is modulated by three individual difference factors – linguistic self-confidence, anxiety, and self-perceived communicative competence. 43 ESL learners from six intact classes worked in self-selected groups during their normal English classes. Each group performed two versions of the same argumentative task – a simple and a complex version. The topics of the discussions were comparable, and the sequence of the tasks was counterbalanced. Twenty-three hours of audio- and videotaped data were collected and coded in terms of global and specific measures of speech production and various interactional features hypothesized to facilitate attention to L2 constructions. Self-report questionnaires were employed to determine the mediating effects of the individual difference variables. Quantitative analyses revealed the following significant trends: When task complexity was increased, participants demonstrated lower syntactic complexity but greater accuracy and lexical diversity. In addition, the more complex task proved more effective in inducing the use of specific, developmentally advanced constructions and in promoting interaction-driven language learning opportunities. However, only slight significant effects were observed for individual differences.