|English schools work under complex New Public Management (NPM) environment, in which teachers are required to collect and use volumes of data for many reasons especially for accountability. Data is thus likely to control the 'life' of English schools with arguments for and against its use. This qualitative case study explored in-depth, how teachers interpret and use data within five English secondary schools. Data was collected via interviews, school documents and questionnaires. Qualitative data was coded into themes in 'NVivo' program in line with the research questions and the conceptual framework of the study. Questionnaire data was analysed descriptively in SPSS program and triangulated with qualitative data for confirmability. For internal and external validity, tables of specific case and cross-case analyses were constructed. The results show four new findings. That is, (1) pastoral data is not a stand-alone data (2) schools do not partner with each other around data use (3) state schools are more constrained in data use than the independent school and (4) data collection and access are hierarchical. Other findings are that English schools collect large amounts of data with most pupil-related data being quantitative to allow ranking and comparison of students' academic and non-academic performance. Teachers also seem to be shifting focus from teaching to data collection and that data collection serves as a form of surveillance where teachers use data to set targets for pupils, monitor and report academic progress to school leaders and parents. Also, there is superficiality in data collection, interpretation and use. For example, teachers use data to determine which pupils should have certain resources as interventions, but the study did not find compelling evidence that teachers use data to improve their teaching methods or to evaluate what they do. Finally, data use in the schools spread through hierarchies from the government to school leaders, middle leaders and class teachers then all the way up again with teachers responding positively and negatively to data use. In terms of support, schools mostly support access and internal collaboration around data. Performativity, as discussed for example by Stephen Ball, has been used to interpret these findings.