Li Kaiwen, a high school student in Beijing, poses with kids in Siem Reap, Cambodia, where she spent her summer vacation as a voluntary worker.

Before leaving for Cambodia to do voluntary work, Li Kaiwen thought she was going to a poor country to offer her help. But, that was only half the story - she gained more from the experience than she ever imagined.

The Chinese high school student remembers trying with all her might to saw some plywood under the scorching sun of Siem Reap. She was sunburned, and beads of sweat rained down her cheeks. Yet she could not get the work done.

A 5-year-old Cambodian boy, seeing her struggling with the wood, ran to her and gently wiped off the sweat on her forehead with his sleeves. He offered to show Li how to saw the wood, which seemed like a piece of cake.

The 16-year-old from one of the best international high schools in Beijing says at that very moment, she felt like an idiot.

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"If both the kid and I were left on a lonely island, the little one would be able to build himself a wooden shelter," she says. "But I, well educated, well fed and raised, would freeze to death."

Many Chinese teenagers who did voluntary work in Cambodia for 10 days during their summer vacation have similar stories. They were among 69 Chinese students who participated in the Cambodia International Service project, aimed at giving teenagers an opportunity to do voluntary work in schools and orphanages in poor regions in Cambodia. They have to pay for the stay themselves.

The program was started in early 2011 and 160 Chinese students have participated so far.

While many of their peers spent the summer touring prestigious universities in Europe and the United States, these young volunteers spent 18,880 yuan ($3,000) each to build houses in Siem Reap.

Li got to know of the project in school after listening to a talk by the program's founder, Xu Jiatian, who shared his experiences of Cambodia. She was thrilled.

"I'm eager to try anything that will help others," she says.

Her decision to do voluntary work in Cambodia surprised both her parents and classmates, who were worried about her safety.

But having been to Cambodia, Li says although the country is poor, it is not as dangerous as expected. She says she will never forget her first impression of Phnom Penh, the capital of Cambodia.

"The children walked on the streets wearing nothing, bare footed," she says. "And as we waved to the people on the streets, they all waved back and smiled at us sincerely."

She also finds that the cows in Cambodia "look like sheep because they are too thin".

"But the country is beautiful, nothing like I'd imagined."

The village she volunteered in, is a six-hour drive from Phnom Penh. The first thing Li and other volunteers did was to stack some plywood to build a new house for an orphanage. Carpenters demonstrated how that was done. Later, they also worked in the fields, growing crops for villagers.

"Almost everyone suffered from insomnia during the first few nights," says Tang Yutong, 18, another volunteer from Beijing. "Our backs and arms hurt so badly during the night because of the hard work in the day," says Tang, who has done three voluntary work tours in Cambodia since 2011.

Both Tang and Li admit they do not have to do housework at home.

Li says what kept them going is the lovely kids who gathered around them, wiped off their sweat and sang for them in the Cambodian language. Some of the girls would sit beside her and braid her long hair while she took a break.

"The kids do not speak much English," she says. "But they paint pictures for us, and write the words 'I love you' on them."

And she can never forget a little boy who was always beside her while she worked and on the day the house was completed, he looked at her in the eyes and said in English: "Tomorrow? You come?"

Li says she burst into tears. The boy continued: "Two? Three?" "He wanted to know if I would be back in two or three days. I could not answer him," Li says. "All I know is I will be back every vacation. Those days in Cambodia have shown me a life that I did not know before."

It has been weeks since Li and Tang have been back from Cambodia. Staying in their air-conditioned homes in Beijing, they still reminisce about the hot but happy days in Siem Reap.

"It feels like being in two different worlds," Li says.

"I used to do things that brought change to my life. But now, I am making changes in other people's lives."