Gordon Brown has warned that the number of children around the world missing out on formal schooling will rise unless the international community takes urgent action.
The former prime minister - who agreed at the end of last year to chair the Global Campaign for Education - has given notice that a big hike in investment is needed if recent successes in primary education in some of the poorest countries are to continue.
Mr Brown told The TES that he is determined the world should meet the United Nations' Millennium Development Goal 2 - that all children, no matter where they live, should have access to primary schooling by 2015.
The commitment, adopted by world leaders in September 2000, has been the subject of increased development aid from many developed countries.
But Mr Brown said the numbers missing out look likely to rise by 2015. "There are still 69 million children not at school and there is a shortage of two million teachers a year," he said.
"There is a major task ahead of us to alert the world to the danger that the number of children not in school will actually rise by 2015 if no further action is taken and new ways found to ensure that this investment takes place in the developing world.
"We don't have the benefits of mass communications, the internet and the new technologies in schools in developing countries. To be honest, we only have half the classrooms we need in Africa."
He said that while many wealthy countries had signed up to the Millennium Development Goals, the global financial crisis was threatening achievements since 2000.
Mr Brown added that the focus of the campaign should be training teachers. "We need to have a better and more co-ordinated system for teacher training because better teachers lead to better education.
"The latest estimates suggest that we need an extra two million teachers trained a year. There has to be some co-operation across borders to make that happen."
But he has not given up hope. "I see a movement of opinion around the world where people are saying that it costs around $100 a year to educate a child in Africa. This is a very small amount to pay for something that is a moral right that is being denied millions of children.
"It is the means through which Africa and the developing world can empower themselves so that they are not dependent upon aid."
- Millennium Development Goal 2: ensure that by 2015 children everywhere complete a full course of primary schooling.
- In the developing world as a whole, 89 per cent of children of primary school age were enrolled in education in 2008, up from 82 per cent in 1999.
- 69 million children worldwide were denied the right to education in 2008.
- Enrolment in sub-Saharan Africa increased by 18 per cent between 1999 and 2008. But almost half of all children not attending primary school live in this region.
The former prime minister used a recent fact-finding trip to Mozambique as an example of the work that needs to be done.
"It does not cost a lot to build a school or a classroom in Africa," Mr Brown said. "I was in Mozambique at a school and the classroom was being used from 6am to 7pm, with four shifts. Children would be getting three hours each at most.
"And then if the light went, the children on the last shift were sent home.
"The children weren't even sitting at desks, they were sitting on the floor. There is a huge amount to be done to deliver the facilities to deliver education, but I believe a co-operative effort can make a difference to achieving it."