A quarter of a billion children worldwide are failing to learn basic reading and maths skills in an education crisis that costs governments $129 billion every year, the UN's cultural agency warned in a report Wednesday.
Inadequate teaching across the world has left a legacy of illiteracy more widespread than previously thought, UNESCO said in its annual monitoring report.
It said one in four young people in poor countries was unable to read a sentence, with the figure rising to 40 percent in sub-Saharan Africa,
The United Nations defines "youth" as people aged between 15 and 24, although UNESCO's definition varies across regions.
"What's the point in an education if children emerge after years in school without the skills they need?" said Pauline Rose, the director of the nearly 500-page Education for All Global Monitoring Report.
In a third of countries analysed, fewer than three-quarters of existing primary school teachers were trained to national standards, while 120 million primary age children across the world had little or no experience of school, the UNESCO report found.
"The cost of 250 million children not learning the basics is equivalent to $129 billion, or 10 percent of global spending on primary education," the report said.
Thirty-seven countries monitored by the report are losing at least half the amount they spend on primary education because children are not learning, UNESCO said.
In developed countries including France, Germany and the United Kingdom, immigrant children lag behind their peers, performing far worse on minimum learning targets.
Indigenous groups in Australia and New Zealand face similar problems, it said.
The report called for global education policies to focus not only on enrolment rates but also on equal access and better teaching.
"Access is not the only crisis -? poor quality is holding back learning even for those who make it to school," UNESCO director general Irina Bokova wrote in the report's foreword.
She said it was clear that the educational targets set in 2000 by the UN's Millennium Developments Goals would not be reached.
Rose said "new goals after 2015 must make sure every child is not only in school, but learning what they need to learn".