Urban schools in Belgium have become increasingly multilingual. This invites pedagogical challenges as pupils struggle with the instruction language, but it leads to ideological anxieties in Dutch-medium schools especially. Recent studies show that Flemish teachers have negative attitudes towards the use of other languages than Dutch. These studies call for anti-bias training and for a teacher education that lives up to the current multilingual reality. There are good reasons however for expecting that teachers will waver ambivalently between linguistic uniformity and diversity, because they associate both ideas with important, albeit competing, educational purposes. Developing positive attitudes towards multilingualism is possible. But the effects of such an endeavor may be limited, and the expectations about what teachers are capable of unrealistic, if it is ignored that teachers will also attend to linguistic uniformity, at least in the present circumstances. Policy debate needs to take into account that teachers have to strike a balance between competing pedagogical purposes and societal concerns. Advocates of multilingualism at school may be more effective if they associate linguistic diversity not just with attitudes of tolerance and respect, but also with knowledge, qualification, and assessment.