Fewer than half of the world’s some six million refugee children are in school, the U.N. warned Thursday, calling on the world to do more to ensure refugee children have access to education as a fundamental right.

A full 3.7 million school-aged refugee children have no school to go to, the U.N. refugee agency said in a report.

“This represents a crisis for millions of refugee children,” U.N. refugee chief Filippo Grandi said in a statement, urging international action to get the children back to school.

Entitled “Missing Out: Refugee Education in Crisis,” the 48-page report’s release comes as the U.N. General Assembly is preparing to host a summit on refugees and migrants in New York next week.

The summit will be followed the next day by a pledging conference for new offers of aid to refugees hosted by U.S. President Barack Obama.

“As the international community considers how best to deal with the refugee crisis, it is essential that we think beyond basic survival,” Grandi said, pointing out that refugees on average are displaced for about 20 years.

That, he said in the U.N. report, “is more than an entire childhood.”

“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.

“Education is also a key contribution to keeping the hope of refugees, and in situations in which despair is so prevalent, going to school, learning, acquiring knowledge and skills, are fundamental,” Grandi told The Associated Press in an interview Tuesday.

Thursday’s report, which compares UNHCR data on refugee education with data from UNESCO on global school enrolment, showed that only 50 percent of the world’s refugee children have access to primary education.

That compares to a global average of more than 90 percent.

“And as these children become older, the gap becomes a chasm,” it said, pointing out that only 22 percent of teens living as refugees attended secondary school.

That compares with a global average of 84 percent.

As for university, only one percent of refugees attend, compared to 34 percent globally, the report showed.

Thursday’s report said efforts by UNHCR and others to enroll 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.

In 2014 alone, the school-aged refugee population swelled by 30 percent, UNHCR said, stressing that at this rate an additional 12,000 classrooms and 20,000 teachers are needed each year to cover the refugee needs.

The fact that a full 86 percent of refugees are hosted in developing countries that are often already struggling to educate their own children complicates things further, Thursday’s report said.

Over half of the out-of-school refugee children are located in just seven countries: Chad, the Democratic Republic of Congo, Ethiopia, Kenya, Lebanon, Pakistan and Turkey, it found.

The situation in war-ravaged Syria meanwhile shows how a conflict can quickly reverse positive education trends, the report said.

Before the country’s devastating conflict began five and a half years ago, 94 percent of Syrian children attended primary and lower secondary school.

By June of this year, only 60 percent were in school, leaving 2.1 million children and teens without access to education, according to U.N. figures.

At the same time, nearly five million Syrians have fled to overstretched neighboring countries where access to education is difficult.

The U.N. estimates nearly 900,000 Syrian refugee children are not in school.