Large quantities of data are now being generated, collated and processed within schools through computerised systems and other digital technologies. In response to growing concerns over the efficiency and equity of how these data are used, the concept of "open data" has emerged as a potential means of using digital technology to democratise data access and use within whole school communities. Drawing on participatory design research in two Australian secondary schools, this paper explores the possibilities of making existing school data openly available in digitised form for teachers, administrators and students to access, interpret and use. The results of these interventions--while only partially successful--provide valuable insights into the technical, informatic, organisational and social issues surrounding the use of data in schools. The paper concludes by considering the practical and theoretical limitations of attempting to democratise data engagement within school settings.