Large quantities of data are now generated, collated and processed within schools through computerized systems and other digital technologies. In response to growing concerns over the efficiency and equity of how data is used, the concept of 'open data' has emerged as a potential means of democratizing data access and use across school communities. Drawing on participatory design research in two Australian high schools, this paper explores the possibilities of making existing school data openly available in digital 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, organizational and social issues surrounding the potentially democratized use of data in schools.