In this paper, we describe one secondary school's radical attempt to rethink the shape and purpose of education for its pupils, and its subsequent return to more traditional methods in the face of pressures of performativity and accountability. Framing our analysis within activity theory and its emphasis on contradiction as a driver for change, we describe the school's move towards a thematic curriculum and "personalised learning" as a process of productive tensions which enabled the development of new approaches to education. While these innovations were considered to be of major benefit to both teachers and pupils, a fundamental contradiction between the focus on individual development underpinning the new approach and the demands of accountability in a persistent culture of performativity proved to be insurmountable. We argue that this particular contradiction highlights the dominance of measurability in judgements of school success and individual progress, with consequences for the pupils' longer term education futures.