This article explores the development of pedagogical content knowledge in relation to one teacher's experience in learning to engage in a Vygotskian approach to teaching second language (L2) pragmatics known as "concept-based pragmatics instruction" (CBPI). The teacher, Mrs. Hanks, was a PhD candidate in second language acquisition at the time of the study, and she was a co-investigator for a larger project that investigated the integration of CBPI into an intact L2 French class that she was teaching. We focus on three aspects of Mrs. Hanks' development: (1) mediation she received during "mentoring meetings" with a more expert collaborator (her co-investigator), (2) changes in her classroom practices during the study, and (3) metacognitive reflections on her progress at the end of the study. Drawing on Vygotskian theory, we examine Mrs. Hanks' development in terms of her internalization and transformation of relevant pedagogical content knowledge. In this way, we are contributing to the very small amount of empirical work examining teacher education/development in the context of "learning to do" concept-based instruction (e.g. Williams, Abraham, & Negueruela, 2013), with specific focus on CBPI.