There is a growing expectation that schools should systematically collect and analyse data as a point of departure for decisions. However, research shows that teachers themselves are less convinced that they need to base their decisions on data, as they mainly rely on their intuition and experience. This article examines the extent to which teachers use data as a source of information for decisions at classroom level and what motivates them to use these data. We will also look at what impact the teacher's decision-making style, supportive relationships and the reflective capacity of the school team have on teachers' motivation for using data. Our research data was collected by means of an online survey of 408 teachers in 52 primary schools in Flanders. The results demonstrate that the quality of teachers' motivation for using data is a key element in promoting data use in schools. Teachers who feel autonomously motivated will make greater use of data than teachers with a controlled motivation. We found that the use of a rational decision-making style by teachers, supportive relationships within the school and the reflective capacity of the school team all lead to an increase in teachers' autonomous motivation for using data.