While several studies have investigated the role of parental school choice in exacerbating school segregation, less attention has been paid to the role of institutional contexts and specific educational policies and regulations. However, since the institutional context sets the framework for both school autonomy regarding the admission process and the actual extent of school choice, it has a significant effect on parents' choices. By comparing two educational contexts that have undergone opposite policy interventions regarding the role of parental choice in school allocation -- Mülheim, Germany and Amsterdam, the Netherlands -- we confirm the idea that expanding parental choice increases segregation levels. However we also suggest that the relationship between education policies and segregation patterns is very complex and dependent on the interactions of various aspects lying within and outside the education system. Both cases reveal that competition between schools and theirdiscretionary scope in admitting pupils also plays a key part.