This study investigated how providing students with opportunities to use diagrams in interactive communication with peers might affect their diagram use and problem solving processes. The participants were 42 junior high school students who were assigned to a condition with peer instruction opportunities (experimental) or without (control). The peer instruction opportunities were designed to facilitate students’ diagram use in communication. The results revealed that, in post-instruction assessments, the experimental participants spontaneously used more diagrams and were more successful in problem solving. No differences were found in the timing with which participants started using diagrams. However, the experimental participants used more appropriate types of diagrams that also incorporated more relevant information. The findings therefore indicate that opportunities for peer communication with diagrams facilitate not only enhanced spontaneity in diagram use but also the construction of more appropriate, detailed diagrams, and these in turn likely contribute to better problem solving performance outcomes.