You'll hear a lot of pieties about China this week. As George Osborne and Boris Johnson schlep from Shanghai to Shenzhen, they'll give the usual sales spiel about trade and investment and the global race. What they won't talk much about is Zhang Lintong. Yet the 16-year-old's story tells you more about the human collateral in the relationship between China and the west than any number of ministerial platitudes.

In June 2011, Zhang and his teenage classmates were taken out of their family homes and dispatched to a factory making electronic gadgets. The pupils were away for a six-month internship at a giant Foxconn plant in the southern city of Shenzhen, a 20-hour train ride from their home in central China. He had no say in the matter, he told researchers. "Unless we could present a medical report certified by the city hospital that we were very ill, we had to go immediately."

As a first-year student at a secondary vocational school, it was illegal for Zhang (not his real name) to be sent on any kind of internship. And under Chinese law work-placements have to be directly related to a pupil's studies. Zhang was an arts major and a fan of the work of Russian realist painters. He was to spend half a year turning out iPhones and other consumer electronics.

The only child of a peasant family in the Chinese countryside, Zhang's first experience of pitching up at a mega-factory was to be split up from his equally bewildered classmates. They were forced to sleep in different factory dormitories, among adult strangers. Given the same uniforms as the regular workers, the interns' training was rudimentary. And then there was the work: Zhang performed one or two small tasks over and over again while standing for hours on end in a huge line turning out Apple products. "It's tiring and boring," he told researchers outside work. "I very much want to quit but I can't."

Incredible as it sounds, Zhang's story is actually typical. As the number one supplier to Apple and manufacturer for a host of other consumer-electronics firms, Foxconn is one of the largest employers in China – and among the biggest users of student labour. In October 2010, the company estimated that, at times, up to 15% – or 150,000 – of its million-strong workforce were students. More than 28,000 were estimated to be interning for Apple alone. Last year, academics reported that 70% of the staff at a Honda gearbox factory were from secondary schools

Nor is such exploitation merely the stuff of recent history: just last week, Foxconn admitted that it had broken the law by making schoolchildren work overtime and night shifts. More than a thousand of them had reportedly been building the soon-to-be released PlayStation 4 games consoles.

Zhang's interview was one of 63 with student interns collected over two years in a forthcoming book by Jenny Chan, Pun Ngai and Mark Selden. The children's stories make upsetting reading. A 16-year-old girl suffers menstrual disorders in the middle of her internship. The pains continue for months, and she thinks they're caused by the night shifts and the stress of the factory: "We don't have breaks whenever we're behind on the production targets." The stranded girl is understandably reluctant to discuss the issue with her male line manager, yet her parents are so far away they can only offer suggestions over the phone.

Such tales aren't just a series of regrettable one-offs. Zhang and his classmates and the hundreds of thousands of teenagers like them are at the heart of one of the most powerful economic relationships at work today. They are part of a trading relationship in which Chinese children are forced into a manufacturing machine, with the connivance of both major employers and local government, to produce shiny things to be sold by billion-dollar multinationals to western consumers.

What do I mean by the connivance of government? The summer before Zhang was packed off to a Foxconn plant, a city in his home province of Henan ordered all its vocational schools to send their students to a Foxconn factory in the same city of Shenzhen. Those who had placements elsewhere were to break them off and rush south.

Chan and her colleagues believe this was to have a ready-trained workforce for the imminent opening of an iPhone plant in Henan. Far from being kept secret, the directive was press released and the provincial governor oversaw its implementation. Official recruitment targets were issued and the local government was offered a £1.6m subsidy to get Foxconn the workers it needed. And teachers went with their classes, paid by Foxconn to make sure their children worked hard and don't leave.

In one factory, the students complained about stomach aches, about choking – and they'd ask about the safety of their workplace. How did their teacher respond? As he later told the researchers, he invoked the nuclear disaster at Fukushima: "Take a moment to think about the selflessness of the scientists and the medical teams [at Fukushima] when Japan reported the tragic radiation leak. None of the Japanese withdrew from rescue work. So everyone of us should take responsibility for the good of humanity." Through this system western consumers get amazing new gadgets year after year. Apple will tell you that the inhumane conditions at its Chinese supplier factories are now safely in the past, even though it admits that some of the internships are still "poorly run". It requires a convenient blindness to believe that. A report by Apple's auditors in May 2013 "found no interns has been engaged at Chengdu [a city in mid-western China] since September 2011". Yet an HR official for Foxconn told Chan in September 2011 that more than 7,000 student interns were working in the Chengdu factory – over 10% of the entire staff.