The campaign for universal primary education has resulted in more children attending schools, but many are not receiving good quality lessons and truancy is rife, education leaders have warned.
John Rendel, chief executive of Promoting Equality in African Schools (Peas), which educates more than 8,000 secondary students in 22 schools in Uganda and Zambia, said that many developing countries had focused on rapid expansion of primary provision at the expense of the quality of the education on offer.
As a result, absenteeism was a problem in many African schools, with the majority of students dropping out of education before they had even set foot in a secondary school, he told TES.
His comments were echoed by Anthony Lake, executive director of children's charity Unicef, who added that of the 250 million fourth-grade children (aged 9-10) who were unable to read or write, half actually attended schools.
"Unless we infuse (the campaign for primary education) with learning and quality, as well as bringing these children into school, we're never going to get the rates of graduation into secondary school and we'll never meet our goal," he said.
The claims come as concern grows over the slow progress towards achieving the United Nations' Millennium Development Goal of free universal primary education by 2015.
The schooling of children in conflict zones has been a particular problem. According to Unicef, 2 million children are out of education in war-torn Syria alone.
Cultural attitudes and financial pressures on families have also proved to be barriers: in the Indian state of Rajasthan, 40 per cent of primary students drop out of education by the age of 11, while across all rural parts of India just one in 100 girls reaches the end of secondary school.
At the World Innovation Summit for Education in Qatar last month, former British prime minister Gordon Brown - now the United Nations special envoy for global education - revealed that 57 million young people were not attending primary school.
"It is possible to imagine 20 million people who are out of school now being in school by the end of 2015," he told delegates. "But that leaves 40 million children who will not be in school unless we change what we're doing."
An extra $6 billion (pound;3.7 billion) must be raised in order to achieve this goal, Mr Brown added.
Although an additional 4 million children have received primary education in the past year, Mr Rendel said that the majority of students in the developing world failed to complete their primary education and received little benefit from their time in the classroom if they did not continue to secondary level.
"Because there isn't credible opportunity to go on to secondary education, a lot more kids drop out of primary education than (otherwise) would and attendance is lower," he said. "There are a hell of a lot more kids in primary school than there were in 2000. This has resulted in two things: a lot of primary education is terrible and there's this wave of kids coming through and not going on to secondary."
Mr Rendel called on developing countries to focus on increasing attendance rates and improving the quality of education in primary schools.
"If you make schools great and parents can see. (that) in the future their kids will be able to look after them or get better jobs or get their family out of poverty, then they will back education. They will keep their kids in school for longer," he added.
However, many countries were keen to point out the effort they were making to improve provision. Angelina Motshekga, South Africa's minister of basic schooling, told TES that the proportion of five-year-olds in education in the country had increased from 39 per cent in 2002 to 85 per cent in 2011. South Africa was also monitoring progress on "equity and quality", she said.