Although previous studies support using pair work in the language learning classroom, some have shown that getting L2 learners into pairs without raising their awareness about the global norms of collaboration will not necessarily create quality opportunities for interlanguage development. In this study, we investigated the contribution of teaching collaborative ground rules through peer modeling to a learner's routine participatory patterns over time. Using a qualitative single case study methodology, we focused on one intermediate EFL learner interacting with different peers in pairs in an intact class. According to the syllabus of the course, learners had to pair up each session (9 sessions in total) with three different partners to do a narrative task. On the fifth session, a model performance with collaborative ground rules knitted into it was demonstrated to the class to find out how the provision of peer modeling would change the pair participatory patterns. Our analyses of the data from the learner's audio-recorded performances prior and subsequent to the modeling session suggest that the provision of peer modeling has qualitatively expanded the learner's interactive patterns in pair interaction. This study contributes to our understanding of collaborative tasks, and it also suggests that peer modeling could be used as a useful pedagogical technique for teaching learners how to collaborate meaningfully in dyadic interaction.