Growing up in mainland China, Hailun "Helen" Zhou always knew that she would finish her high school education in America, whatever the cost.

"That's what everybody does," said the 17-year-old from Sichuan province who has spent the last two years studying in California and will be graduating this spring. "My father's friends all sent their kids abroad, so that was the trend."

Zhou is among a growing number of Chinese teens who are flocking to US high schools, looking for a western education and a competitive edge in gaining admission to US universities and then finding a job back home.

But the pursuit of the American dream can quickly turn into a nightmare, experts warn, as many of these so-called "parachute kids" live in the US with little parental supervision and can end up in trouble -- and even in prison.

"It's a huge industry," said Joaquin Lim, who runs a company that helps place Chinese students in American schools. "The last figure I read put it at 25 billion dollars."

Of nearly one million international students enrolled in public and private institutions in the United States in 2014-2015, about 304,000 -- or 31.2 percent -- were from China, according to the Washington-based Institute of International Education.

Some 30,000 of those students attended secondary schools, compared to fewer than 1,000 a decade ago.

The majority of these "parachute kids" aged between 14 and 19 land in southern California. For the most part, they attend Catholic or Christian schools because of restrictions by the US government on foreign student enrollment at public schools.

In cities such as Murrieta, a rural community about 80 miles (130 kilometers) southeast of Los Angeles, the number of Chinese students has ballooned in recent years, bringing welcome cash to the school district as well as host families who care for the teens.

- 'It's an investment' -

"It costs about 50,000 dollars a year for the parents, who are mostly middle class, to send their kids here but they consider it an investment," Lim said.

"Three years ago, we had about 40 Chinese students enrolled in high schools in Murrieta and today we have more than 300 and the number keeps growing."

The sleepy town of about 105,000 residents, many of them retirees, is a far cry from China's polluted mega-cities, but most of the teens adjust well to American life, said Renate Jefferson, who oversees the exchange program for the public school district.

"What they notice first is the blue sky," she said. "They just walk around in awe at the blue sky. They think it's beautiful."

The students are also baffled by the freedom they enjoy academically and the artistic outlets available to them -- a welcome change from the rigorous, numbers-obsessed learning system in China.

"If there is one word to describe life here, it's the word 'free'," said Junheng "Carl" Li, 19, who is graduating this year from a Catholic school in Murrieta.

"You have a lot of choices and much more freedom to study what you're interested in."

- Shady intermediaries, no supervision -

But many of the "parachute kids" whose parents rely on shady intermediaries to help them through the bewildering application process are in for a hard landing in America, ill-equipped to navigate the cultural transition and their newfound independence.

Last month, three Chinese teens enrolled at a private school in Rowland Heights, a neighborhood east of Los Angeles that has a large Chinese diaspora, were given stiff prison sentences for attacking two other teens.

A judge at the preliminary hearing said the case reminded him of 'Lord of the Flies' - the 1954 novel by William Golding about a group of schoolboys stranded on a desert island who turn feral when forced to fend for themselves, local medai reported.

The incident attracted widespread attention in China and prompted soul-searching on the wisdom of sending teenagers to a foreign country with no close parental supervision.

"You don't send your child 6,000 miles before verifying the school and who they are staying with," Lim said. "Too often, these kids are thrown into a completely foreign environment and are not prepared to fend for themselves."

Police sergeant Steven Perez, who was involved in the Rowland Heights case, said officers are increasingly finding teens out on their own at night or even living in homes bought by their parents with little or no adult guidance.

"You basically have kids who are managing themselves and have no one to answer to," Perez said. "Or you have kids basically renting a room where they are residents and they are not accountable to those people either."

Evan Freed, an attorney who represented one of the Rowland Heights teens who was sentenced to 13 years in prison, said the case should serve as a wake-up call to parents that they could be setting their kids up for disaster rather than a bright future.

"As my client told the court -- she felt lost, she felt sad that her family wasn't here and that she basically took advantage of the freedom that she had," Freed said.