In order to prepare effective writing teachers, teacher educators need an understanding of how preservice preparation programs, inservice professional development, and the policies and practices of K-12 schools work together to influence teachers’ writing instruction. This qualitative case study uses complexity theory (Davis & Sumara, 2006) to analyze how one teacher learned to teach writing within and through the emergent, nested, interacting systems of teacher education and the school where she took her first teaching job. Data sources were fieldnotes of her teaching and interviews about her instructional decisions, which were coded using constant comparison (Glaser & Strauss, 1967) and the theoretical lens. Findings indicate the teacher’s understanding of writing instruction emerged through interactions between systems as she reproduced and recombined the ideas, values, goals, and activities she encountered within her undergraduate and graduate courses, her school district, and her sixth-grade classroom. The study concludes with discussions of the dynamics of learning to teach writing that emerged through the research and the implications of these dynamics for teacher education, educational policy, and future research.