In this study, the researchers investigated the effects of shared and different first language (L1) background, L1 use amounts, and peer familiarity on the frequency of language-related episodes (LREs) and task scores in interactive pair work. By exploring these variables in distinct interactions, the authors attempted to obtain a more fine-grained picture of peer interaction patterns and develop strategies to facilitate short interactive tasks. The study's recordings of the same-L1 dyads were translated to explore whether the participants stayed on task and why they used their L1. Forty-two intermediate students of English as a second language (ESL) from various L1 backgrounds recruited from a U.S. university participated in the study. They were placed into four dyad types: same-L1/familiar, same-L1/unfamiliar, different-L1/familiar, and different-L1/unfamiliar. Each dyad completed a short interactive spot-the-difference task. Peer familiarity positively affected the production of LREs and task scores, but no clear differences were found between the same-L1 and different-L1 dyads. The researchers also found evidence that peer familiarity affected the same-L1 and different-L1 dyads differently. The dyads stayed on task the entire time, using L1 for task management or vocabulary deliberations. Finally, strong negative correlations were found between L1 use amounts and both LREs and task scores.