Current attention in L2 acquisition research focuses on the integration of message-focused and form-focused instruction. One way to accomplish this is through the incidental focus on form during meaning-focused activities. Some studies have investigated incidental focus on form in different contexts and shown that it exists in L2 classes and facilitates L2 acquisition. This study investigated the effects of interactional patterns (teacher-learner and learner-learner) on several features of incidental focus on form (types of focus on form; types of feedback; linguistic forms focused on and types of immediate uptake). The data from over 10 h of task-based interaction revealed a significant difference in the types of form-focused episode (FFE) that occurred between the two interactional patterns. In terms of the type of feedback provided, no difference was found between the teacher and learner interactional patterns but a difference in uptake responses between the two interactional patterns was revealed. The study notes that, in both teacher-learner and learner-learner interactions, incidental FFEs occur frequently, and that the high frequency of immediate uptake facilitates opportunities for L2 learning. Because learners were able to work as an effective knowledge source for each other, spoken interactions should be encouraged between learners in the L2 classroom. (Contains 8 tables.)