In many developed countries, disagreement on important policy issues between groups with different social identities ('ideological polarisation') is increasing. In professional settings, these disagreements undermine cooperation and trust between employees, which negatively affects work relationships and managerial decision-making. We investigate whether people with more education tend to express attitudes that are more (or less) polarised. Using nationally representative data for 18 OECD countries from 2010 to 2018, we find that in most countries, ideological polarisation between liberals (political left) and conservatives (political right) on three key policy issues (income inequality, immigration and gay rights) increases with education. This 'education-polarisation' gradient varies across countries, is strongest in the United States and is linked to stronger alignment between political ideology and non-political values, and greater internet use among more-educated individuals. This finding can explain why polarisation can persist and even increase, despite the growing availability of information. We conclude with implications and recommendations for higher education.