To support teachers in implementing ambitious reform efforts, professional developers and teacher educators need to know more about teachers' thinking about argumentation. Specifically, there is a need to understand more about teachers' views and evaluations of "students'" mathematical arguments as they play out "in practice." In this article, we share a tool developed to elicit teachers' pre- and postevaluations of students' mathematical arguments on a problem-solving task. We discuss the design of the tool and provide evidence of its utility. Our findings indicate that the tool can be used to (a) identify changes in teachers' evaluations of student mathematical arguments over time and (b) inform the design of professional learning experiences.