A case study of a beginning teacher in an urban high school, conducted over five years including one preservice year and the first four years of teaching, describes how the teacher came to understand and amend her assessment practices through guided questioning of student work. The protocol poses questions to engage teachers in discussions about the development of assessments, the impact of mandates, expectations for pupil learning, and future modifications. The case study, part of a larger university research project designed to understand the process of learning to teach, confirmed the value of using a guided inquiry interview protocol to help beginning teachers become reflective practitioners.