We undertook a research project consisting of four interrelated studies, in order to shed light on ways educational professionals make sense and make use of educational data in general and school performance feedback in particular. Theoretical insights illuminate why a sensemaking perspective is an appropriate and valuable lens to study data use. These insights are complemented with concrete findings from empirical research conducted within the context of the Flemish national assessments. By zooming in on data users' sensemaking processes and on factors that impact these processes, we intend to demonstrate how a sensemaking perspective helps us reflect on existing gaps between external provision of data, practitioners' data use, and intended effects in terms of school improvement.