Kim Euntae · Jung Hyerin This study explores the practical knowledge of a teacher who taught an expository writing class for three years, using the collaborative autoethnography research method. As a result of the study, the teacher was aware of the problems in exposition methods and textbook composition, reconstructed them in his own way, and practiced classes. In addition, the teacher emphasized and endeavored to promote student agency, but simultaneously exhibited conflicting attitudes toward it. While observing students’ writing material selection and writing performance, the teacher recognized the limitations of existing assessments and gained an expanded awareness that performance assessments could be used as a means to provide students with opportunities for growth. These examples illustrate how teachers find a balance between their educational beliefs and the constraints of reality and how they solve problems through reflective practice. In this context, teachers can enhance their expertise and develop practical knowledge by reflecting on their teaching practices and addressing classroom problems. More effort is required to bridge the gap between theory and practice in the field through research on teachers’ practical knowledge of teaching and learning.