Governmental education policies provide vague, general confines in which local actors have to design concrete policies tailored to their needs. Such policies rely on the local capacities of schools for implementing them. Recently, qualitative studies reveal that a great deal of variation in policy enactment should be attributed to school contextual variables. This study adds to these findings by examining to what extent school contextual variables influence the implementation of one type of education policy in Flemish schools: school-based language policies (SLP). It combines quantitative survey data from 28 primary schools with focus group interviews in a subsample of six schools in order to verify whether and why the school context affects the implementation of SLP. Results confirm that school context does affect implementation. Particularly, the ethnic composition of the student population is one of the main motivations for school teams to implement an SLP, and this is often associated with a deficit perspective.