Teacher professional development in writing is an increasing area of interest due to the complex nature of the profession including learning needs of students and the demands of external assessment regimes in the contemporary landscape. However, professional development often denies the contextual experiences and expertise of teachers in favor of prescriptive top-down approaches. This paper contributes to the literature on effective teacher professional learning by showing how co-design between teachers and researchers can have an impact on student learning. In this study we focus on professional learning for the teaching of writing in the elementary classroom context, working with third grade students in the age range of 8-9. Through a reflexive analysis of multiple data sets including student writing samples, interviews, classroom observation footage, and teacher testimony, this study reveals the importance of teacher confidence in enabling students to view themselves as writers with a clear audience and purpose. The findings show how positioning teachers as research partners throughout a co-design process of professional learning benefits both students and teachers as it provides authentic, contextualized and creative approaches to teaching writing and improved writing outcomes for students.