Zhang Fuyou teaches nine students at Dajiang Primary School at Dalong town of Lipu county in the Guangxi Zhuang autonomous region.

Over the past 38 years, he has scrapped more than 10 wooden boats. After the boat becomes too decayed to sail, he turned the boats into beehives to raise bees. His village house, built with mud bricks, thatch and wood, is surrounded by more than 100 beehives.

He sells the honey for extra income and buys a new boat, every four years, which costs 2,500 yuan (about $400).

All of his nine students, from grade one to grade three, are left-behind children, whose parents work in neighboring Guangdong province as migrant workers, leaving them with their grandparents at home. Zhang and his 58-year-old colleague Lu Xingping call themselves "left-behind teachers".

They had many chances to leave the school to teach in a better school. "If we leave, the children will probably drop out of school," Zhang says. "We live in nearby villages. So we are obliged to stay," echoes Lu.

Both Zhang and Lu feel it is more difficult to teach the left-behind children, especially the left-behind ethnic minority students. There are two Yao ethnic group students in their classes.

"The left-behind children are invariably more shy and timid than kids living with parents," says Zhang. "They need special care from the society. Their teachers are their only 'society', apart from their grandparents. We 'left-behind' teachers have an important role to play."

Five-year-old Wei Qiaolin is the youngest pupil in the school. Her grandmother Lin Xiujuan, 70, comes to school to take her home. Qiaolin refuses to walk the two hours back home after a tiring school day. With tears in her eyes, she tells her grandmother that her feet and legs are too painful to walk.

"She did not speak a single word or smile all day," says Zhang. "Her grandpa was an old respected teacher here. But her grandparents' love cannot replace her parents'."

Lin stays overnight with her granddaughter in the school for the night. Zhang and Lu prepare a room for young students and their grandparents to stay over when they cannot go home because of illness and bad weather.

"Compared with the children's sufferings, my boat work is not worth mentioning at all," Zhang says. "Their parents authorized me to punish the children physically. But I cannot bear to do so."

Zhang's two children work as migrant workers in Lipu. His farmer wife lives with their son and helps to take care of their grandson in the county.