Bringing about school improvement in economically poor urban contexts remains a major challenge. In England the emphasis on competition between schools has further complicated this agenda. At the same time, there is evidence of the emergence of a new policy emphasis that involves support and challenge to school-led improvement efforts through collaboration with other schools. This paper provides an evaluative account of an attempt to use such processes of networking across all secondary schools in one city. The study suggests that schools working together can contribute to the raising of aspirations and attainment in schools that have previously had a record of low achievement, but that this is never a straightforward process--schools are complex organisations, and collaboration between them involves the orchestration of action and purpose at many levels. The paper concludes that the successful use of such approaches involves dealing with a number of challenging dilemmas, and draws out the implications for policy development.