School leaders are faced with the daunting task of anticipating the future and making conscious adaptations to their practices, in order to keep up and to be responsive to the environment. To succeed in a rapidly changing and increasingly complex world, it is vital that schools grow, develop, adapt and take charge of change so that they can control their own futures. This paper will examine the tension that exists for school leaders in relation to data about their schools and their students, arguing that the explicit connections between data and large-scale reforms make it impossible to avoid a critical approach to data, drawing on research in Ontario and Manitoba in Canada, and examining parallels with evidence from research in England, to highlight the challenges involved in using data effectively in different political contexts and mandated policies on the uses of data.