In 2013 UNESCO reported that there were 28.5 million out-of-school children (OOSC) of primary school age in countries affected by conflict, half the total number of OOSC worldwide (UNESCO, 2013). However, this does not tell us about the number of children who are being denied an education as a result of conflict, or the impact that conflict has on education systems. This study sets out to quantify this impact and seeks to arrive at estimates of the order of magnitude of the costs of conflict to education: both in terms of the human cost, represented here by the number of OOSC, and the financial cost in terms of physical damage done to education structures and through loss of human capital. As well as drawing on international evidence from the global literature, the research included case studies of three conflict-affected countries: the Democratic Republic of the Congo (DRC), Nigeria and Pakistan. These three countries were selected because they had the largest numbers of OOSC, and together were home to half of all OOSC living in conflict-affected countries in 2011. Findings from the three case studies are included throughout Sections 2 and 3 of this report.