In 2008, he started his undergraduate economics degree at Renmin University of China, and joined the China Youth Network, a youth volunteer organization that delivers sexual education and social skills education for young people.

Founded in 2004 as a group predominantly focusing on university students, CYN later branched out to deliver training to young children of migrant workers and left-behind children in rural areas, under the leadership of Gaoshan and his peers.

Unique to the CYN model is peer-to-peer training, meaning that lessons are delivered by young people themselves, ensuring training is open, candid and relevant.

Over a period of two years, CYN trained 40 capable children of migrant workers in Beijing, Shanghai and Hangzhou, and left-behind children of Chongqing and Changchun, who in turn delivered lessons to about 2,000 other children.

The left-behind children typically stay with their grandparents, seeing their parents just once or twice a year.

Some migrant workers who take their children to urban cities end up sending their children to migrant schools, which are unofficial schools opened by teachers without teaching qualifications. These parents, who have rural hukou－or household registrations－have gone to urban cities to work. But their rural hukou means they need to pay a premium to send their children to urban schools, which they cannot afford.

Gaoshan said children of migrant workers are under a lot of pressure. Their parents work very hard to pay for their education, and have high expectations for them to study hard and achieve results. At the same time, they face pressure from society, which treats them as second-class citizens.

"There is a lot of peer pressure, a lot of gang culture and bullying. They sometimes don't have siblings and don't know who to talk to when they have mental pressure. There is no psychological counseling," he said.