This article draws upon, but also critiques, activity theory by combining analysis of how an activity theory derived research intervention attempted to address both everyday work practices and organisational power relationships among children's services professionals. It offers two case studies of developmental work research (DWR) interventions in UK local authorities, wherein multi-professional teams were attempting, at operational level, to develop and stabilise new work practices. Data are derived from the series of interviews and DWR workshops conducted in each research site. The data analysis draws attention to the ways in which multi-professional innovations and professional development were sometimes constrained by managerial structures that were still embedded in "traditional" professional silos. The paper also offers conceptual discussion of activity theory's potential shortcomings in addressing "vertical" divisions of labour and the contradictions embedded in relationships between operational staff and their senior managers.