In the context of renewed interest in teachers' identities as writers and the writers as artist-educators, this paper reports upon the findings of "Teachers as Writers" (2015-2017). A collaborative partnership between two universities and a creative writing foundation, the study sought to determine the impact of writers' engagement with teachers on changing teachers' classroom practices in the teaching of writing and, as a consequence, in improving outcomes for students. The project afforded opportunities for writers and teachers to work together as learners in order to improve student outcomes. The study involved two complementary datasets: a qualitative dataset of observations, interviews, audio-capture (of workshops, tutorials and co-mentoring reflections) and audio-diaries from 16 teachers; and a randomised controlled trial (RCT) involving 32 primary and secondary classes. The findings reveal that the teachers' identities and assurance as writers shifted significantly. The Arvon experience also led to pedagogic shifts which the students reported impacted positively upon their motivation, confidence and sense of ownership and skills as writers. However, these salient dispositional shifts did not impact upon the young people's attainment. The professional writers gained new understandings which substantially altered their conceptions of writers' potential contribution in schools.