YANTAI, China – The five schoolboys weren’t of legal age to work on an assembly line. But when their vocational school sent them to a Foxconn manufacturing plant last month as part of an internship program, they were soon piecing together Sony PlayStations 12 hours a day.

One boy said he worked an overnight shift that started at 7:30 p.m., looking for imperfections on finished gaming consoles. Another struggled to stand after spending hours screwing together thousands of devices. The intern assigned to lug plastic cases for the product bore red welts on his neck from hoisting heavy loads on his thin shoulders.

The baby-faced laborers were all 15 years old – a year younger than the legal age to perform such work in China. Speaking to a Los Angeles Times reporter, all five said that a day before their three-month internships began, company employees visited their school requesting copies of everyone’s identification cards.

“They knew how old I was, but they didn’t say anything,” said one of the teens, who is in his second year at the Yantai Engineering & Technology College, a vocational school in this industrial seaside city in eastern Shandong province. The Times is not disclosing his or his schoolmates’ names because the teens fear repercussions.

Their internship ended abruptly this month after Chinese state radio reported that interns as young as 14 were working at the plant. In a statement issued Oct. 15, Foxconn admitted using an undisclosed number of underage interns; it pledged to prevent it from happening again.

Foxconn Technology Group, a Taiwanese manufacturing giant, rose to prominence producing electronics for leading brands including Apple, Sony and Dell. More recently it has made headlines for a spate of industrial accidents, alleged labor abuses, worker riots and suicides.

The controversy also highlights the role of China’s vocational schools, which labor activists say are paid by companies to provide them with low-wage factory hands.

“The basic point of the system is to provide cheap labor to manufacturers,” said Geoffrey Crothall, a spokesman for China Labour Bulletin, a Hong Kong nonprofit promoting workers’ rights. “Ideally, you go to vocational school to learn a trade so that you’re in a good position to get a job when you graduate. In reality, the vocational schools make money by sending kids to factories. It’s a fairly manipulated form of labor available to manufacturers whenever they need it.”

Foxconn declined to comment beyond its earlier public statement.

Chinese law allows youngsters younger than 16 to work in a limited capacity, but not in potentially dangerous jobs such as those on assembly lines, labor experts said.

A Sony spokesman said Foxconn had assured the company that no underage workers were used to manufacture Sony products in Yantai, but said it would press Foxconn to investigate.

Foxconn jobs are still highly coveted by migrant Chinese workers, many of whom insist that conditions and pay are better there than at rival factories. But international pressure by labor groups and clients, as well as a spate of critical news reports, have prompted changes.

At the behest of Apple, Foxconn this year submitted to an outside audit of three of its Chinese factories by the Washington-based Fair Labor Association. (The audited factories did not include the one in Yantai, which reportedly does not make Apple products.)

In response to the audit findings, Foxconn committed to a host of improvements, including the treatment of interns, who it says account for fewer than 3 percent of its 1.2 million employees in China. The company pledged to verify student ages and put young workers in appropriate positions. It also agreed to limit the work day for interns to eight hours.

The Fair Labor Association said its audit did not discover any workers under 16 at Foxconn factories in Guanlan, Longhua and Chengdu.

Students at China’s vocational schools generally are required to complete work internships to graduate, a condition that makes it tough for them to refuse assignments. Although interns are compensated by the companies that employ them, they aren’t afforded the same rights as adults under Chinese labor laws, according to China Labour Bulletin’s Crothall.

Many vocational schools are run by local authorities, who are eager to help major employers such as Foxconn fill their assembly lines, especially during peak production periods. In return, vocational schools are paid about $100 for each intern they provide to a factory, according to the New York-based China Labor Watch.

The Yantai Engineering & Technology College attracts youngsters out of middle school who forgo high school in hopes of joining the work force sooner. The school’s 12,000 students learn to operate earth diggers, program software and fix engines, depending on what program they choose. Annual tuition is about $575.

Internships usually take place during a student’s second year. Teachers are supposed to accompany the interns, but Yantai students said none was present during their recent Foxconn stint.

An assignment at the LG Electronics plant across the street from the school was considered a plum internship, students said, because the tasks are largely mechanized. In contrast, the youngsters said they dreaded getting sent to Foxconn because the long hours, physical demands and monotony were well known among the student body.

“None of us wanted to work there, but we had no choice,” said another of the interns, a lanky 15-year-old with a peach-fuzz crew cut who was assigned to put finished PlayStations into boxes. “You can’t fight the school and the system.”

The boys said they were given a day’s notice to pack their belongings and head for Foxconn, which picked them up in company buses for the 15-minute drive to the factory. They said they received little training before starting their assignments.

The five bunked together in a dorm room they said was more comfortable than their housing at school. They said they netted about $150 each for the first month of work – after the company deducted $80 for their lodging and cafeteria meals.

“The work is too tiring,” said the teen who pulled the overnight shift. “It’s really unfit for our age.”

The five boys said they had never seen a PlayStation 3 before. Told what it was for, one of the boys said he asked Foxconn staff if he could buy one. “They said ‘no,’ so I asked if I could get one in China, but they said it was for export only,” the boy said.

The teens said Foxconn never explained why their internships ended so abruptly. The five returned to their school and said they pieced together what happened after reading news reports on Twitter-style micro-blogs.