The contribution of data use in schools has been proven via visible changes in policy and practice in schools (instrumental effects), changes in practitioners learning or cognition (conceptual effects) and changes in opinions or attitudes regarding teaching or policy-making (symbolic effects). Nevertheless, limited research is available on the extent to which data use in schools results in the aforementioned effects and how they can be explained by data use expectations and collaboration. This paper addresses both issues by describing and explaining data use effects via a large-scale study in Flanders. Data collected from 1472 teachers indicate that, although teachers are moderately positive about the extent to which data use results in different types of effects, data use effects cannot be taken for granted. Structural Equation Modelling (SEM) shows that explicating data use expectations and data use collaboration are essential in order to facilitate data use effects in schools.