The past 20 years have seen the steady 'datafication' of school systems -- i.e. the rendering of key aspects of school practice into data that is digitally collected, processed and circulated. In contrast to assumptions of 'data-driven' schools as sites of more efficient and automated forms of data work, this paper examines the extensive human labour that now supports data production within schools. Drawing on in-depth interview data generated within three Australian secondary schools, the paper explores three distinct stages of data production involving the increased labour of teachers, school leaders, administrative and technical staff, parents and students. These findings highlight how the production of digital data within schools is associated with heightened levels of human labour -- from formally recognised activities to less visible infrastructural maintenance and 'repair' work. The paper concludes by discussing how 'school data' corresponds with broader tensions relating to school working conditions, occupational cultures, employment relations and worker organisation. Rather than being a source of more efficient and machine-led work with data, the increased prevalence of digital data seems to perpetuate some of the less desirable features of schools as workplaces.