Some equate being a left-behind child to being a problem or mentally disturbed, and say that it would be difficult for them to move up the social ladder.

But 27-year-old ZhangJuan is challenging those stereotypes.

Born in Guiping county, Guangxi Zhuang autonomous region, Zhang used to be a typical left-behind child.

Her parents－two of China's 277 million migrant workers－took Zhang and her elder brother to Guangzhou, Guangdong province, when they were babies. The parents couldn't find work, so they sold rice door to door without a business license.

When Zhang was 6 years old, her father had to take her back to Guiping because the tuition for migrant workers' children was more than 5,000 yuan ($770) a year, well beyond their reach.

When Zhang entered fifth grade, her father left for Guangzhou again, as the family could barely afford tuition for two children.

Zhang and her brother had to survive on their own.

"Once I had a fever after midnight. I had no one around but my brother," Zhang recalled. "In darkness, he just put me on the back seat of his bike and rode about half an hour to the emergency room."

When summer came, Zhang and her brother had to go to Guangzhou to help their parents sell vegetables in wholesale markets. They also cooked for their parents.

"We used to stay through the night in huge vegetable wholesale markets," Zhang said. "There was no place to sleep. So we just put some gunnysacks together and took a nap on them."

Despite these challenges, Zhang now works for the Beijing Children's Legal Aid and Research Center, China's first NGO dedicated to offering free legal services to children.

Zhang is in charge of a public welfare program, which helps left-behind children in kindergarten by providing training to teachers and giving them free computers and projectors.

Zhang said the biggest secret is "effective communication".

"No matter where my parents are, they always keep in touch with us," Zhang said. "Even in the early days, when making phone calls was not convenient, we would talk at least once a week."

The talk was more than a daily greeting. Zhang and her brother discussed in detail their progress and concerns in their studies. And unlike many parents－not just migrant workers－Zhang's would also tell them specifically what they encountered in Guangzhou, about their rice and vegetable sales, about their happiness and sorrow, about everything, she said.

"Through talks like that, I learned that my brother and I were not abandoned. We were loved," Zhang said. "Our parents worked hard to put food on the table and keep us in school. We want to study hard."

So they did. Zhang got into Northwest University of Political Science and Law, with a major in criminal investigation. Her brother entered Dalian Maritime University and became an engineer at Guangdong Electric Power Design Institute.

Zhang's father is no longer working, while her mother works as a housekeeper.

Zhang has invited some 350 kindergarten teachers to the training program in Beijing for the past three years. This year she added something new to her project－encouraging parents to do video chats with their children more often, an inspiration that came from her own experience.