Determining what students know and understand, as well as what misconceptions they have, is essential to planning and providing targeted intervention and support. In this article, a teacher uses formative assessment interviews to uncover evidence of students' understandings and to plan targeted instruction in a mathematics intervention class. The authors present an example of a student interview, a discussion of the benefits and challenges of conducting interviews, and actionable suggestions for implementing them. This narrative highlights the benefits of conducting interviews with students by using formative assessment probes and offers some implementation suggestions.