This study investigates conditions designed to optimize learning where professionals utilize the expertise and support of one another. It describes a research--practice collaboration to enhance teacher knowledge and practice through peer observation of, and feedback about, classroom practice in writing. A collaboratively designed observation guide, containing key elements of effective practice in teaching writing, helped focus classroom observations and discussions. The feedback-after-observation discussions, aimed at improving practice, were facilitated through employing principles to help ensure the conversation maximized learning. All teachers at a school (11 pairs) engaged in seven rounds of observation and feedback over one year. Several data sources tracked progress and outcomes including observation ratings and notes; post-feedback discussion questionnaires; and written responses during professional learning meetings. Data show that most feedback discussion contained specific change or enhancement messages and, over time, the degree of specificity increased. There was evidence for the utilization of feedback in the form of changed practice. Perceived usefulness of feedback varied. The process of observing and engaging peers in dialogic feedback was challenging. Teacher responses confirmed the need to build content knowledge about writing and writing pedagogy, together with skills to engage in professional learning conversations to promote and support changed practice.