This classroom-based study explored language mindsets in the context of communicative interaction between L2 learners. Amid the increasing research on mindsets in the L2 field, two issues warrant further research to improve our understanding of how mindsets affect L2 learning. First, research has largely been product-oriented and mindsets' impacts on learning processes are under-investigated. Second, the research has rarely examined actual behaviors, especially in an interactional context. Participants were university-level EFL learners in Chile (N = 42). They were paired according to their mindsets, resulting in three pairing patterns and seven pairs for each pattern: Growth-Growth (G-G), Growth-Fixed (G-F), and Fixed-Fixed (F-F). During regular classes, the pairs engaged in decision-making tasks. Two propensities were focused upon. First, problem-solving behaviors were operationalized as language-related episodes (LREs) in which learners worked together to solve linguistic issues. Second, collaborative learning was analyzed using Storch's framework of the degree of collaboration. In total, 384 LREs were identified. The comparisons among the three pairing patterns showed that (a) growth-mindset learners tended to initiate LREs, (b) F-F pairs engaged in the least number of LREs, and (c) G-G pairs resolved the most LREs proportionally. However, growth-mindset learners did not necessarily engage in collaborative interaction and some exhibited negative behaviors (e.g. negative perfectionism). Together, the study suggests that while growth-mindset positively contributes to problem solving, the individually-held beliefs do not necessarily translate to social contexts such as peer interaction in the classroom.