This study investigated collaborative dialogue in terms of patterns of interaction, use of L1 and language-related episodes (LREs). These elements were analyzed as to different pairings and task complexity. To that end, two different levels of student pairs were sampled (high-high [H-L] & high-low [H-L]) from the preparatory class of a foundation university. In addition, three different task types were used (word formation task, error correction task and composition task) in the study. The results showed that in both pairings (H-H & H-L) collaborative pattern was observed. As to L1 use, it was more prevalent in highlow (H-L) pairing and the composition task required more use of L1. Moreover, L1 metatalk was used more than its metacognitive function. In terms of LREs, H-L pair experienced more episodes and the composition task required more LREs than other tasks. The study suggests that collaborative pattern, irrespective of language levels of pairs, secures effective interaction and transfer of knowledge between learners. Also, it is suggested that L1 use and LREs can be mediating tools for these interactions.