Research on writing pedagogy education (WPE) emphasizes the importance of engaging graduate student instructors (GSIs) in mindful reflection about their own practices and about composition theory. Little research, however, has explored what we learn from a systematic, empirical investigation of GSIs' reflective writing. In this article, we describe a writing assignment we created for a graduate composition theory course that required GSIs to connect their own beliefs and experiences with the theory they read. We analyzed 60 essays to learn how new writing teachers understand and use composition theory. Our analysis shows that GSIs rely on three discursive patterns to write about theory (we call these "cite-comment, cite-apply, cite-engage") and adopt three orientations towards theory (using theory "to explain prior beliefs and maintain a teacherly identity, to solve classroom problems and shore up a teacherly identity," and "to accept uncertainty and become a reflective teacher"). We discuss connections between GSIs' discursive strategies and their theoretical orientations. We conclude by sharing how we have revised both this assignment and our training program to help GSIs better engage theory as they reflect on their own experiences. Finally, we explore the implications of what we learned for WPE broadly.