Three boys aged 11 to 13 attacked and killed a teacher and robbed her of a cellphone and a few hundred dollars in cash in southern China, state media reported Tuesday.

The state-owned Beijing News said the boys were hanging out around an elementary school in the township of Lianqiao in the province of Hunan on Sunday when they decided to rob the only teacher guarding the school.

The boys — who are students at other schools — beat the 52-year-old teacher with a wood stick, stuffed her mouth with cloth and dragged her into a bathroom, where she died, the Beijing News said.

The report said the students ran away with the teacher's cellphone and about 2,000 yuan ($330) in cash. They were arrested on Monday.

A police officer reached by phone confirmed the case but declined to give more details. He gave only his family name, Yang, which is customary with low-ranking Chinese officials.

Other media reports said the three boys were "left-behind" children, which means their parents are migrant workers who go to more industrial Chinese cities for jobs and leave their children in their hometowns under the care of others, often their grandparents.

China's rural areas have tens of millions of left-behind children, and their wellbeing has become a major social concern.