One in four young people in developing countries is unable to read a sentence, according to a new report. Poor quality education has left a "legacy of illiteracy" more widespread than previously believed, it warns.
Unesco, the UN's educational, scientific and cultural body, suggests that 175 million young people lack even basic literacy skills.
Today there is an urgent need for new investment in adult literacy
"Access [to education] is not the only crisis - poor quality education is holding back learning even for those who make it to school," said Unesco director-general Irina Bokova in a foreword to the 11th annual Education for All Global Monitoring Report, which measures progress towards international goals.
An estimated 250 million children are not learning basic reading and maths skills, according to the report, even though half of them have spent at least four years in school.
This "global learning crisis" costs developing countries billions of dollars a year in wasted education funding.
Adult illiteracy has remained stubbornly high over the past decade. In 2011, there were 774 million illiterate adults, a decline of 1 per cent since 2000. This figure is projected to fall only slightly, to 743 million, by 2015.