This study describes the initial implementation of the writing component of the "Write to Read" ("W2R") literacy intervention in eight low-SES (socio-economically disadvantaged) elementary-level urban schools. Through customised onsite professional development provided by coaches, the writing component sought to build teachers' capacity to design and implement a writing workshop framework infused with research-informed practices for writing suitable for their school and classroom contexts, including attention to cognitive, social and affective dimensions. The paper draws on quantitative and qualitative questionnaire data gathered from classroom teachers in the eight schools in Year 1 (n = 66) and Year 3 (n = 62) of implementation, and semi-structured interviews with randomly selected teachers in each school in Year 4 (n = 18). In general, teachers succeeded in implementing a writing workshop approach to teaching writing, within the broader W2R literacy framework, including the allocation of more time to writing instruction. Professional development, including observation, feedback and demonstration by W2R literacy coaches, contributed to high levels of teacher confidence in such areas as planning and teaching fiction and non-fiction writing genres, and analysing writing samples to inform mini-lessons. By Year 3, teachers noted marked or good improvements in students' attitudes towards writing, volume of writing produced, knowledge of writing genres, and language of response to writing. Areas in need of further support included aspects of the craft of writing, including writing vocabulary, supporting pupils to set goals for writing, selecting mentor texts to teach writing genres, and using a rubric to assess writing development.