Educational systems across the globe are attempting to reshape the vertical and horizontal dimensions of school accountability. The vertical dimension involves devolution of responsibility to individual schools while the horizontal typically entails promoting the professionalism of leaders and teachers through school networks and school-to-school pairings. In many systems, these shifts occur within an environment of high-stakes accountability. Little is known about the ways that high-stakes consequences for individual schools shape the translation of professional practice across schools. The study reported here traces the diffusion of data-informed practices in a formal pairing of two primary schools in England--a school ranked as "outstanding" and a school in "special measures," a persistently low-achieving school. Study findings trace the ways in which the threat of consequences under which the low-achieving school operates shapes the diffusion of professional practice across schools. The study details how the lead school brokered, or mediated, state requirements, co-constructing the supported school's narrative of improvement. Findings from this study illuminate the ways that vertical relationships within the system of schooling influence horizontal relationships across schools. Clarifying the shaping of professional practice across schools is increasingly critical as patterns of provision of schooling proliferate and the links among the state and schools become increasingly complex.