The report by the Britain-based Save the Children added that hundreds of thousands of displaced children are struggling to enroll for school in their host countries and in Syria.
The report spotlighted how Syria's conflict, now entering its fourth year, is denying a decent education to a generation of children, with consequences that may last for generations.
Within Syria, the report estimated that 3,465 schools, or one-fifth of the country's educational buildings, were either destroyed or damaged, or are being used for military purposes.
Syria's civil war has killed at least 190,000 people, according to the U.N. Nearly three million Syrians have fled the country.