Population-control measures mean some big cities are making it increasingly difficult for the children of their least-privileged residents to enroll in the public school system, resulting in an exodus of students. Wang Xiaodong and Zhao Xinying report.

A long with Beijing's other primary and middle schools, the Dandelion School opened for a new semester on Tuesday. However, only 520 of the 549 registered students, all from migrant worker families, returned following the Spring Festival holiday, teacher Zhao Kai said.

"We learned that 23 students had transferred to other schools, mostly back in their hometowns, but the other six, mostly seventh-graders, did not return," Zhao said.