How might pre-service elementary teachers' misconceptions of proof and counterexamples influence their teaching of proof? To investigate this question, two types of interviews--task-based and scenario-based--were designed to elicit pre-service elementary teachers' (PSTs) conceptions of proof and counterexamples and how those conceptions might impact their instructional decisions. A qualitative analysis of the data revealed that these PSTs had difficulties following or constructing formally presented deductive arguments and understanding how deductive arguments differ from inductive arguments. The data also revealed that the misconceptions that pre-service teachers held played an important role in their instructional decisions. [For the complete proceedings, see ED597799.]