This paper explores the impact of external accountability on four mechanisms of network-internal quality control and the properties of (mandated) inter-organizational networks. An explorative case study approach examines the external accountability of a newly established educational network (MAT) and how schools and the Trust are held accountable by the English Inspectorate of Education, Ofsted and the Department for Education (DfE), through Regional Schools Commissioners (RSCs). Analysis of documents and interviews were used to reconstruct a sequence of events over a period of five and a half years. Our findings indicate that the combination of accountability activities led to more centralized control over, and monitoring of curriculum, assessment and school improvement. This was accompanied by a pause in the growth of the Trust and the establishment of a regional structure of school collaboration. As accountability is particularly organized around individual school performance (through Ofsted inspections), this limited development of internal mechanisms of quality control around network-level outcomes. A short-term focus dominated the allocation of resources to schools in special measures or with an upcoming inspection visit. In the discussion, an alternative model is presented for network-level accountability and a set of indicators for effective accountability of collaborative arrangements.