Providing primary education for all children around the world is helped rather than hindered by fee-charging schools, an education expert has said.
The UN says 115 million children miss out on going to school
Professor James Tooley of the University of Newcastle says many poor children in developing countries are taught effectively in private schools.
He says calls by charities and the UN to abolish fees are misguided.
The United Nations is meeting on Wednesday to debate its target for universal primary education by 2015.
The cause of primary education for all is one of the UN's millennium goals - with the ambition of giving an education to an estimated 115 million children who currently miss out.
About 80% of these children live in sub-Saharan Africa or southern Asia.
The UN says the problem is most acute for children from poor families - and that enrolment and attendance in school can be increased by "reducing or eliminating school fees".
But Professor Tooley says pursuing education for all by stopping fee-paying schools is "backing the wrong horse".
He says research shows that private, rather than state schools are already providing an efficient service to many poor families in India and in African countries.
These private schools are "academically more effective than state schools, and achieve higher results at only a fraction of the cost," says Professor Tooley.
And he argues that using the private sector - and recognising its current role - will make universal primary education "much easier to achieve than is currently believed".
As an example, he says that in Lagos State, Nigeria, international agencies believe that 50% of children do not have school places - but in practice the number without places is only 26%, because the remainder are attending unregistered private schools.
And he raises questions about the success of universal free education when it means the closure of some private schools and enrolment in "overcrowded state schools".
But these arguments run against calls from the Save the Children charity, which last week said that abolishing fees would remove barriers to school for many children, especially girls.
In a report, the charity said that in 17 of the 25 countries with the most girls not in education, fees were being charged by schools.
It said another 4.5 million children would go to school if fees were abolished in 13 countries in sub-Saharan Africa.