As many as half of all Syrian children are not enrolled in school, and in some places the rate is as low as 6%. The gaping holes in their education could cost the country as much as 5.4% of its GDP annually (or $2.18 billion) in the long-term and create an environment that’s ripe for further unrest, warns a new report from rights group, Save The Children.

Before the war, virtually all Syrian children were enrolled in primary school and the literacy level for young people was very high. Today, the country has one of the lowest enrollment rates in the world, with nearly 3 million children missing out on their education. Half of all refugee children are not attending school, and in Lebanon, where most of the refugees have settled, that number is nearly 80%. At least a quarter of Syria’s schools have been destroyed or repurposed during the conflict. Save the Children estimates that repairing the damage and training new teachers to replace those who had left the country or been killed would amount to $3.2 billion.

The impact on this “lost generation” could be far reaching. Before the war, children in Syria who did not finish elementary school earned one-third less than those who finished secondary school, and 56% less than those who graduated from university. The war could further exacerbate this disparity.

It might also contribute to a vicious circle of conflict in the future. Research has shown that inadequate schooling, which leads to low-paid jobs or unemployment, can create a pool of recruits for militant groups promising a better life.

Save the Children is calling on the international community to fund efforts to put the country’s education system back on track.