The report says 9.3 percent of China's school-age migrant children are out of school, with 46.9 percent of six-year-olds yet to start school.

China's Compulsory Education Law requires children over the age of six, regardless of gender or ethnicity to attend school. In some areas where conditions are poor the children can start school at age seven.

The report finds "overage" elementary school students to be a serious problem among migrant children. Migrant children aged 13 who are still in elementary school account for 31.5 percent of students. By that age they should be in secondary schools.

The study also finds that more than 60 percent of the children between the ages 12 and 14 who are out of school have already started working.

By the end of 2004, more than 6.4 million rural children of compulsory education age were living in cities with their parents. Another 22 million rural children remain in their family's rural homes, while their parents worked in cities, according to the Ministry of Education.

Children who were brought to cities by their migrant parents are often charged school fees that are much higher than those charged by schools in rural areas. The large number of school-aged migrant children living in cities is straining urban education resources.

Numerous private schools for migrant children have been established in cities which are often criticized for ill-equipped, lacking infrastructure and qualified teachers.

In July, the Haidian Education Commission of Beijing forced 37 private schools for migrant children in the district to close and reassigned the 15,000 affected students to nearby public schools.

The report called for attention from governments and all social sectors to improve education policies for migrant children to secure their right to receive compulsory education.