Consistent with the notion of learning as changing participation (Lave & Wenger, 1991; Rogoff, 1998; Sfard, 1998; Young & Miller, 2004), the present qualitative study investigated how social interaction between learners of Japanese as a foreign language and native speaker classroom guests contributed to the students' use of second language (L2) linguistic resources in their productive performance over time. Specifically, the study considered the kinds of L2 linguistic resources that were made available to learners during guided interpersonal interactions with native speaker guests. Findings suggest that participants' nonpedagogical interaction with a more knowledgeable native speaker interlocutor provided a wider range of linguistic resources than instructor-fronted instruction and that those linguistic forms were taken up by the learners and then appropriated in subsequent activities with peers.