This article provides a conceptual basis for a teacher preparation course designed to improve the writing skills and teaching practices of in-service teachers. To propose this course, we first examined the research on preparing all secondary in-service teachers to use writing well. Research suggests that teachers' histories as writers greatly affect whether they feel confident enough to use writing with their students. Even though many teachers believe in the value of using writing for instructional purposes, they report significant challenges--namely, a lack of professional preparation and time. Given our experiences as graduate faculty members in a large university, we discuss the need for the graduate-level course that we developed. The curricular design is described, and student survey results suggest that the course is effective. Implications for in-service teacher preparation and professional development are presented in light of recent calls for writing reform.