A report commissioned by the UN education agency says at least 250 million of the world's 650 million primary school age children are unable to read, write or do basic mathematics.
The report launched Wednesday found that 130 million are in primary school but have not achieved the minimum benchmarks for learning, and almost 120 million have spent little or no time in a classroom.
The report for UNESCO, the UN Educational, Scientific and Cultural Organization, by an independent research team said investing in teachers is key.
In about a third of countries, it said, less than 75 per cent of primary school teachers are trained according to national standards.
"While more children are in school, it's been at the cost of quality," UNESCO's UN representative Vibeke Jensen said.
