Presented at AERA'18. Abstract: There is growing interest in reflection and the value of reflection activities in enhancing students’ metacognitive abilities. Reflection effectively connects thinking and doing, building students’ understanding both of what they know, and how to activate that knowledge in their future work. In this study, we explore the formation of students’ design identity as scaffolded by a reflection blog in a graduate human-computer interaction program. Data include 1619 posts and 2019 comments posted by 144 students across three consecutive semesters of an introductory graduate interaction design course. Our analysis demonstrates how designerly talk among students may influence understanding and performance in their future practitioner roles. Implications for professional identity formation, and the role of reflection in this process, are considered.