Using the same specialist terms in online discourse can indicate knowledge overlaps between partners. However, linguistic overlaps do not automatically ensure overlaps in conceptual representations. In particular, learning situations, which typically focus on knowledge acquisition, require a sufficient understanding of domain-specific concepts. This study investigated how the same versus different lexical encodings of specialist concepts influenced peer-to-peer online discourse behavior and information exchange. Student dyads communicated via email while preparing a written text. Partners in each dyad received different texts containing either the same terminology across texts or different terminology. Results showed that dyads in the different-terminology condition communicated more intensively (e.g., clarifying the conceptual meaning of specialist terms by asking questions and giving explanations) than those in the same-terminology condition. However, despite exchanging more information, learners in the different-terminology condition were less certain about their conceptual understanding. Implications for the use of specialist language in peer-to-peer learning situations are discussed. (Contains 3 figures and 7 tables.)