The design of educational institutions has long been seen as a key element in determining social divisions. This article examines the long-term impact of separate and integrated education on relations between the two religious communities (Catholics and Protestants) in Northern Ireland. Using a large-scale survey, the results suggest that in comparison to their previously separate counterparts, individuals who attended an integrated school are more likely to be understanding and respectful of the culture and traditions of others. The finding holds even after a range of background characteristics are taken into account. The results have implications for the role of segregated educational institutions in ameliorating religious, ethnic or racial division in other post-conflict societies. The Northern Ireland evidence suggests that a segregated school system rather than ameliorating intolerance and division may end up exacerbating and reinforcing it.