Ji Siniu poses with her students at the Nujiang Special Education School following their performance at a celebration. Provided to China Daily

In some families, mothers kept giving birth to more children in the hope of having a "perfect baby" if the older ones had some physical flaws, says Ji. "It's sad for such families as they might end up with more than one child who is physically or mentally challenged," she says.

"Unfortunately, this group of kids have been overlooked and some mute kids don't have a name but are called yaba (meaning mute in Chinese)," says Ji.

Related: Teaching with hope

It is common for parents to stop teachers from taking their children to school, even though no school fees are required, Ji adds.

Some parents insist that their children should stay at home to cook while the adults are working in the fields.

Nujiang, surrounded by Gaoligong Mountains and other mountains, has one of the most dangerous roads in the province and it is a tough task to visit students' families. Frequently, Ji and her colleagues have to ride a horse or take the ropeway to overcome the intricate and perilous roads to find a school-age child in tucked-away households in the mountains.

"The kids at my school have learning difficulties. While other kids master a gesture after teaching them once, my students require more than nine or 10 times of gesturing before they get it," Ji says.

Some children in the schools have dramatic mood swings as they do not know how to express their emotions like other children. Some will abuse themselves because they are stressed out and even hit the teacher. But she is motivated and recharged to continue her thankless job whenever some of the students address her as "mother".

Because of staff shortage, Ji and her colleagues have to offer six classes each day, which leaves little time for their families. "Sometimes, I can't differentiate my identity as their teacher or mother after spending 10 hours a day together," says Ji.

According to the regulation on special education by the Yunnan Provincial Department of Education, the proportion of teachers and students at special education schools should be one teacher to four students, on average. But, Nujiang Special Education School with a student population of 99, has only 11 teachers, including the head master.

The school is not losing hope. Her student He Jiyuan, now 30, has returned to teach at the Nujiang Special Education School after graduating from Beijing Union University. "He is an excellent teacher in arts and mathematics, making me believe that all these years have not been a waste of time but an enterprise for my life," adds Ji.

Guo Anfei and Li Yingqing contributed to the story.