Scholars have identified a new configuration of spatial inequality in several of the largest cities in the developing world. This configuration, which I label interspersion, is characterized by the general proximity of classed spaces, particularly ‘slums’ and ‘enclaves’. There is disagreement about how interspersion affects class relations. One side argues that it worsens class relations by foreclosing substantive class interaction; the other side maintains that it improves class relations by enabling greater class interaction. I argue that it is not the extent but the form of class interaction that matters. Interspersion worsens class relations by promoting categorically unequal interaction. It provides regular opportunities for the imposition of spatial boundaries on slum residents. Regular experiences of boundary imposition deepen their sense of discrimination. This argument is based on an ethnographic study of the relations between slum and enclave residents in Metro Manila.