This paper considers the subjectivation of students in light of the increasing amounts of digital data that are now being produced within schools. Taking a lead from critical data studies and the sociology of numbers, the paper draws on staff interviews in three Australian secondary schools to explore the various types of student data being generated, and the forms of student subjectivities that result. In particular, the paper contrasts the 'holistic' possibilities that some school leaders and administrators ascribe to data in terms of expanding the capacity to 'know' students, against the limited ways that data is actually being used within the schools. Most notably, the paper details how digital data appears to be configured within schools' official data procedures and practices to build student subjectivities and position students in narrow terms of performance and attendance. The paper also highlights how teachers make practical use of these limited data 'profiles' in a relational manner -- as a way of stimulating dialogue with students to know them better, rather than a source of precise calculation. In this sense, the paper considers how 'data' might be reframed in educational discourse as a practical starting-point for teacher inquiry and professional judgment rather than an imagined source of all-encompassing knowledge.