At a conference in 2000, the United Nations made equal access to education a five-year goal. But the finding that girls are 90 million of the 115 million children around the world not going to primary school shows little has been achieved, the BBC reported.
The report said that girls still do not have an equal claim on education in 46 countries.
Officials said that poverty, the spread of AIDS in Africa and civil and international conflicts are among the reasons for children not going to school. Cultural attitudes ensure in many countries that available classroom seats go to boys.
"Education of children, especially girls, is the cornerstone to national progress," UNICEF Executive Director Ann Veneman said. "It leads to greater economic productivity, reduced infant and maternal mortality, and a greater likelihood that the next generation of children will go to school."