Northern Ireland has a deeply divided education system with demarcation most notable along ethno/religious and social class lines. The former is largely attributable to the historical organisation of the schools estate based on religion, and the latter is associated with a system of academic selection that filters children into grammar and non-selective post-primary schools according to their performance in tests taken during the final year of primary school. Academic selection, and the grammar school system that underpins it, has come under some considerable scrutiny, with much of the research evidence pointing to a negative relationship between the selective system and equality of opportunity in education. The suitability of this system in a transitioning society that has become more ethnically diverse in post-conflict years has, however, received less attention. Drawing on social cohesion theory, we reflect on the grammar school system to argue that the cross-community class interests animating it not only perpetuate inequalities within respective communities but may also present a significant barrier to peacebuilding efforts in education, and ultimately impede progress towards a more socially cohesive society.