A full 3.7 million school-aged refugee children have no school to go to, the UN refugee agency said in a report.
"This represents a crisis for millions of refugee children," UN refugee chief Filippo Grandi said in a statement, urging international action to get the children back to school.
His comments came ahead of the first-ever UN summit on refugees and migrants, to be held in New York on September 19, and which will be followed the next day by a pledging conference for new offers of aid to refugees hosted by President Barack Obama.
That, he said in the UN report, "is more than an entire childhood."
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"Education enables refugees to positively shape the future of both their countries of asylum and their home countries when they one day return," he stressed.
Today's report, which compares UNHCR data on refugee education with data from UNESCO on global school enrolment, showed that only 50 per cent of the world's refugee children have access to primary education.
"And as these children become older, the gap becomes a chasm," it said, pointing out that only 22 per cent of teens living as refugees attended secondary school.
That compares with a global average of 84 per cent.
As for university, only one percent of refugees attend, compared to 34 per cent globally, the report showed.
Today's report said efforts by UNHCR and others to enrol more refugee children in school were being overshadowed by soaring numbers of newly displaced people.
While the global number of school-aged refugees remained fairly stable at around 3.5 million during the first decade of the 21st century, it has swelled on average by 600,000 children and adolescents annually since 2011, it pointed out.