The purpose of this study was to investigate the impact of pair interaction on the process and product of collaborative writing through analysing Language Related Episodes (LREs) and students' writing products. Four pairs (nine to 11 years old) represented four different patterns of interaction. The results show that the pattern of dyadic interaction influenced the quantity and quality of LREs and associated post-writing. When learners engaged in collaborative or expert/novice patterns of learning, they were likely to produce more LREs and attain higher quality in the post-writing. Both a novice learner and a passive learner benefitted from collaborative writing by watching how the other student wrote. However, students who showed a dominant role had the least improvement in the post-writing. The findings of the study suggest that the interaction patterns affect both the process of collaborative dialogue and second language learning itself.