Armed conflicts around the world are denying 28 million children an education and exposing them to targeted attacks on schools, according to a major study published by Unesco.
School-aged children are also at risk of widespread sexual violence and other human rights abuses, the global monitoring report found.
Attacks on schools in Afghanistan rose sharply to 613 in 2009, up from 347 the previous year, the report said.
It also highlights attacks in northwest Pakistan and Yemen that have led to hundreds more schools being damaged, destroyed or looted.
The report comes as the UK Government announces an overhaul of its aid spending that will target money on war-torn countries.
The Government has pledged to meet a UN target of spending 0.7 per cent of GDP on aid by 2013, with contributions to hit #163;11 billion by 2015, but aid is to be phased out from 16 countries including Cambodia, Angola and Russia.
The Unesco report said that the world is not on track to achieve by 2015 a series of 'Education for All' targets set by 160 countries in 2000.
Countries affected by conflict are likely to miss some of the goals by a "wide margin", it said.
Of all primary-aged children not enrolled in school, 42 per cent live in war-torn countries.