Attacks by Islamic extremist group Boko Haram in north-eastern Nigeria and neighbouring countries have forced more than one million children out of school, heightening the risk they will be abused, abducted or recruited by armed groups, Unicef said.
The United Nations children's agency said the conflict has forced 2,000 schools to close, some for more than a year, in Nigeria, Cameroon, Chad and Niger.
Some have been looted or set on fire by the militant group, whose name means "Western education is sinful".
Insecurity also prevents teachers from going back to classes, while in schools that have reopened, classrooms are overcrowded.
Boko Haram's insurgency has killed about 20,000 people and displaced millions, according to Amnesty International.
Manuel Fontaine, Unicef's west and central Africa regional director, said: "The conflict has been a huge blow for education in the region, and violence has kept many children out of the classroom for more than a year, putting them at risk of dropping out of school altogether.
"The challenge we face is to keep children safe without interrupting their schooling.
"Schools have been targets of attack, so children are scared to go back to the classroom, yet the longer they stay out of school, the greater the risks of being abused, abducted and recruited by armed groups."
Temporary learning spaces are being set up, but security remains a challenge, the agency said.
About 600 teachers have been killed during Boko Haram's six-year insurgency, it added.