United Nations Secretary-General Kofi Annan has called for girls around the world to be given access to schooling.
Kofi Annan is leading calls for global equality
He said this was vital to increase economic activity, cut mortality rates, improve nutrition and prevent the spread of Aids/HIV.
Mr Annan's comments follow the publication of a report by the Global Campaign for Education (GCE), which reveals that 65 million girls around the world are not attending school.
It also finds more than two-thirds of the 860 million illiterate adults are women.
Mr Annan said: "If we are to succeed in our efforts to build a more healthy, peaceful and equitable world, the classrooms of the world have to be full of girls as well as boys.
"Every year of schooling completed by them will be a step towards eradicating poverty and disease."
The World Bank Group has set a target of halving the number of people living on US $1 a day or less by 2015 as one of its Millennium Development Goals.
To achieve this, it has called for equal rates of schooling for the two genders by 2005.
In high-income countries, 95% as many girls as boys attend primary and secondary schools. But in sub-Saharan Africa the figure is just 60%.
Mr Annan said: "To educate girls is to reduce poverty. That is the lesson that unites us today.
"We come to this lesson well-prepared. Study after study has taught us that there is no tool for development more effective than the education of girls.
Parts of Africa have poor rates of girls' schooling
"No other policy is as likely to raise economic productivity, lower infant and maternal mortality, improve nutrition and promote health, including the prevention of HIV/Aids.
"No other policy is as powerful in increasing the chances of education for the next generation."
Mr Annan's remarks come as the GCE, an international coalition of charities, including Oxfam and Save the Children, begins an event involving schools in more than 100 countries.
The World's Biggest Lesson, also backed by former South African President Nelson Mandela, sees students around the world being taught the same lesson - about girls' right to education.
The GCE estimates that a $5.6bn (£3.8bn) donation by wealthy governments each year would be enough to provide universal schooling.
A spokesman said: "Getting girls into school is literally a matter of life and death.
"The children of women who have completed primary education are on average twice as likely to survive beyond the age of five, and half as likely to suffer from malnutrition.
"The benefits are enormous. The obstacles must be overcome."