While participating as a mentor teacher in a professional development project, Alison Vickery, a middle school teacher, developed a strategy: claim-rule-connection (CRC). The "claim" was the answer or response to the question; the "rule" was the theorem, fact, or proof; and the "connection" was an explanation of how the rule applied or connected to the claim. Vickery's strategy for making argumentation more explicit in her classroom used the CRC framework to guide students in justifying their mathematical reasoning. The examples presented in this article describe the strategy and come from workshops with urban secondary teachers who were learning the CRC strategy, observations of Vickery's eighth-grade algebra class, and student work collected as part of a larger project.