"When we were asked what special education was in our first class at a normal university, 40 of us gave more than 20 answers", said Zhao Changhong, now a teacher at a special school in Beijing's Xicheng district.

Zhao, 44, had no idea what kind of students she would face when she was allocated to the special education class of a normal university in Beijing's Fengtai district in 1991.

"Careers like teacher, doctor and accountant were steady for graduates in our generation," she said. "That was my only concern for choosing a major."

However, the first internship in their freshman year doused the enthusiasm of Zhao and her classmates. As they arrived at a newly built special education school in Beijing, the future teachers, full of enthusiasm, were greeted by a hail of small pebbles dropped by a group of mentally disabled teenagers.

"Later that day, we fell silent in our dormitory; some even missed dinner," Zhao said, recalling her frustration at the first sight of her special students.

That early, unpleasant experience left Zhao reluctant to meet students ahead of her second internship, in her sophomore year, but her attitude changed the moment she saw an ardent student clumsily helping a teacher lift chairs during a class she was observing.

She was touched by the role of special education and discovered a sense of mission to make a difference for mentally disabled children.

As a result, she was one of approximately 30 classmates who opted to become special education teachers after graduation in 1994.

According to a report released by the Ministry of Education in 2015, there were 48,125 special education teachers in China by the end of 2014, making the teacher-student ratio in special education 1: 3.86, compared with 1: 4.19 five years earlier.

Zhao has now taught in special schools for 24 years, encountering a number of impressive students, as well as parents, along the way.

Parents have complicated feelings for their mentally disabled children, Zhao said. They hide their anxiety elsewhere, but, lacking another channel to vent negative emotions, reveal their inner feelings to teachers, or question them.

Zhao said she regarded parents' encouragement of teachers as more valuable than affirmation from schools, and it was a child's progress that would dispel parental doubts.

"I will never forget what a mother said to me, 'Having you in my son's life is the best fortune for him'," Zhao said, choking back tears.

As society has gradually become more understanding about children with mental disabilities, communication with parents has become easier. Support from governments and social groups has also increased, with the Ministry of Education report saying total funding for special schools hit 9.59 billion yuan ($1.38 billion) in 2014.

In special investment programs in 2008 and 2012, the central government poured a total of 10.2 billion yuan into building and renovating 1,182 special education schools, 62 higher vocational colleges for the disabled and normal universities for special education, along with improving infrastructure and purchasing rehabilitation equipment for special education. By the end of 2014, there were 2,000 special schools in the compulsory education system.

The report said there were about 395,000 students studying at special schools in 2014.

Special curricula and textbooks have also been set for mentally disabled students, even though they are not universally applicable.

"As we cannot find two leaves exactly the same in the world, the situation of each student with autism varies," Zhao said. "More than 20 types of methods have been summarized to educate mentally impaired students, but we still need to learn from practice when it comes to autistic children."