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The results of the international school tests - known as Pisa tests - are to be published by the OECD on Tuesday. In previous years, South Korea has been one of the highest achievers. But it means long hours of study.

Hye-Min Park is 16 and lives in the affluent Seoul district of Gangnam, made famous by the pop star Psy. Her day is typical of that of the majority of South Korean teenagers.

She rises at 6.30am, is at school by 8am, finishes at 4pm, (or 5pm if she has a club), then pops back home to eat.

She then takes a bus to her second school shift of the day, at a private crammer or hagwon, where she has lessons from 6pm until 9pm.

She spends another two hours in what she calls self-study back at school, before arriving home after 11pm. She goes to bed at 2am, and rises in the morning at 6.30am to do it all over again.

How on earth does she cope with such a punishing schedule?

"I get tired usually but I can forget about my hardships when I see my results, because they're kind of good!"

She says she would like to get more sleep but it's her job to overcome it. To get the qualifications to follow her dream career as a teacher she has to work hard she says, and besides she likes studying, and learning new things.

Hye-Min is not alone. For South Korean teenagers a double shift of school, every week day, is just a way of life.

South Korean parents spend thousands of pounds a year on after-school tuition, not a private tutor coming to the home once or twice a week, but private schooling on an industrial scale.

There are just under 100,000 hagwons in South Korea and around three-quarters of children attend them.

Hye-Min's mother Yoon-Gyeong Hwang says she worries about her daughter, but they have no choice when it comes to having to compete.

"Korea has few natural resources, we don't even have much land, the only resource we have is people. So anyone who wants to be successful really has to stand out. As a mother I don't feel comfortable about this kind of situation, but it's the only thing she can do to achieve her dream."

This relentless focus on education has resulted in formidable exam performers.

How would they compare with pupils who take the GCSE in England, Wales and Northern Ireland?

As a quick test, a group of six teenagers - 15 and 16 year olds - from Ga-rak High School, Hye-Min's school, tried several questions from one of this year's GCSE maths papers.

All of them finished the questions in half the expected time, four scored 100%, the other two dropped just one mark. They then went on to do some more questions just for fun.

It's the sort of performance that makes education ministers in the UK and beyond look on with envy, and has them actively remodelling the curriculum and exams to try to emulate them.

The huge investment in education has also resulted in an economy that's grown at an astonishing rate since the end of the war with North Korea 60 years ago.

South Korea has in two generations gone from mass illiteracy to being an economic powerhouse. Brands like Samsung and Hyundai, Daewoo and LG are internationally known. The country has built itself up through the sheer hard graft of its people.

But it's come at a big cost. The relentless pressure means Korea holds another much less enviable record, that of having the highest suicide rate of industrialised OECD countries.

The most common form of death for the under-40s is suicide. The government understands the pressure, and in 2008 a curfew of 10pm was imposed on hagwons in Seoul. The Education Minister Nam Soo Suh said the government was trying to redress the balance:

"Korea has achieved miraculous growth within a short period of time. I think no other country has achieved such rapid growth within a half century as Korea. And naturally, due to that, we focused on and emphasised achievement within schools and in society, so that students and adults were under a lot of stress, and that led to high suicide rates.

"We still have a long way to go but we are doing some soul-searching in our society, and our goals now are about how to make our people happier."

Prof JuHo Lee, himself a former education minister, and now an academic at the KDI think-tank in Seoul, says intensive education may have been right while Korea was growing its economy, but now it's time for a new strategy.

"Test scores may be important in the age of industrialisation, but not anymore. So we look into the ways to reform our education system, not based on test scores, but based on creativity and social and emotional capacities," says Prof Lee.

South Korea's success is built on an extraordinary work ethic that has delivered rich economic rewards, but that's exacted a heavy price from its people and particularly its children.

It's a price the country is now gradually starting to weigh up.