An Islamist insurgency has kept about one million children out of school in Nigeria and three neighbouring states, the UN children's agency has said.
More than 2,000 schools were shut, while hundreds had been attacked, looted or set ablaze, Unicef said.
Boko Haram's six-year insurgency has devastated north-eastern Nigeria, and has spread to Cameroon, Chad and Niger.
Nigeria's President Muhammadu Buhari gave the military a deadline of the end of the month to defeat the group.
But it is likely to be extended as Boko Haram is still bombing areas despite losing towns under its control in March, says the BBC's Bashir Sa'ad Abdullahi in the capital, Abuja.
The insurgency is said to have killed some 17,000 people and left more than two million people homeless.
Our correspondent says many schools in north-eastern Nigeria, especially in Borno state, have turned into camps for those who have been forced from their homes.
Boko Haram has also targeted schools because of its opposition to Western education, which it believes corrupts the values of Muslims.
In April 2014, it abducted more than 200 girls from a boarding school in north-eastern Chibok town, an incident which drew international attention to the insurgency.
Our correspondent says the north-east has always been seen as one of the poorest parts of Nigeria with low levels of education, and the insurgency has worsened the the social and economic crisis in the region.
In September, Borno governor Kashim Shettima said $1bn (£670m) would be needed to rebuild infrastructure destroyed in the insurgency.
Boko Haram at a glance:
- Founded in 2002, initially focused on opposing Western-style education - Boko Haram means "Western education is forbidden" in the Hausa language
- Launched military operations in 2009
- Thousands killed, mostly in north-eastern Nigeria, hundreds abducted, including at least 200 schoolgirls
- Joined so-called Islamic State, now calls itself IS's "West African province"
- Seized large area in north-east, where it declared caliphate
- Regional force has retaken most territory this year