Building on the cognitive and interactive perspectives of task research, the cognition hypothesis states that increasing task complexity promotes greater interaction and feedback and thus facilitates second language (L2) development (Robinson, 2001b, 2007a). To date, very little research has explored this claim during learner-learner interactions in English as a foreign language (EFL) classroom contexts in which a task-based syllabus is implemented. The purpose of this study was to examine the effects of task complexity on the occurrence of interaction-driven learning opportunities and question development in such a classroom context. Korean university students (N= 191) from four intact English classes were randomly assigned to one comparison group and three experimental groups with various task-complexity levels (i.e., simple, +complex, and ++complex) based on Robinson’s framework. Their interactions were audiorecorded, and occurrences of learning opportunities, operationalized as language-related episodes (LREs), were identified. Question development was identified between pretest and posttests on the basis of the learners’ stage advancement using Pienemann and Johnston’s (1987) developmental sequence. Results indicated that more complex tasks promoted a greater number of LREs and particularly led to LREs targeting developmentally advanced question structures, which result in question development.
