While some recent pioneering work (e.g., Eslami-Rasekh, 2005; Eslami & Eslami-Rasekh, 2008; Yates & Wigglesworth, 2005) has begun to investigate the effects of instructional pragmatics in teacher education, little has been explored in depth as to the way in which teacher cognition develops in the classroom discourse of language teacher development. This ethnographic case study describes the co-constructed development of teacher cognition as it relates to pragmatic awareness documented during a professional development seminar that focused specifically on instructional pragmatics. The seminar was a five-hour component in an intensive 30-hour teacher development program for re-certifying secondary teaching licensure in Japan. Following Vygotsky’s sociocultural theory of learning (Vygotsky, 1978; Johnson, 2009), the pragmatics-focused seminar was built on interaction among participants and the instructor. Data consisted of seven of the participant teachers’ documents, the instructor’s field notes, and recordings of the teacher development seminar. The findings and analysis will place a particular focus on the process in which one of the teacher’s pragmatic awareness was challenged, co-constructed, and reshaped in interaction through a critical learning episode (Kiely & Davis, 2010). Implications of this study include the effectiveness and limitations of the efforts to promote instructional pragmatics with an intention to further explore effective teacher development in this area.