Excluding children from school education could cost the global community around $10 trillion a year by 2030 if states do not take decisive action, the United Nations warned in a new report published on Monday.
The report by the UN's educational, scientific and cultural agency UNESCO estimates the specific costs for private individuals, states and societies, while factoring in lost tax revenues and lower incomes.
It compares the current situation with a scenario in which there are no or only a minimum number of children who leave school early.
According to the Paris-based agency, around 128 million boys and 122 million girls are currently excluded from school worldwide.
Some 57% of the world's children have not acquired basic skills. According to the report, the highest costs of a lack of schooling related to gross domestic product are likely to be in sub-Saharan Africa.
The assessment also points to other social consequences of a lack of schooling, such as more homicides and assaults. Every year that girls spend at secondary school also reduces the risk of child marriages and underage pregnancies, it notes.