Sitting at an upright piano in a small white cubicle, Cho Yun-je pauses from practising her prelude and starts counting on her fingers, “Korean, English, Chinese characters, maths, singing and piano.” The list she reels off with ease does not refer to the subjects on her school timetable – but the extra-curricular classes she attends almost daily at a string of cram schools.

Yun-je is eight years old and a typical representative of South Korea’s schoolgirl population – from the cute pink glasses and blue plastic hairclips in her bobbed hair down to the long list of subjects she studies at after-hours cram schools. South Korea has emerged as a global leader in hothouse education. Hand-in-hand with its rapid transformation from agricultural society to fast-paced industrialised nation over the past half a century has been the development of education. Today, the country regularly tops global education rankings, with supporters including Barack Obama, who earlier this year lauded its education system as the best in the world.

Such successes are rarely attributed to the public education system alone: instead after hours private tuition – often in the confines of cram schools known as hagwon – have long played a crucial role. More than 70 per cent of all schoolchildren in South Korea attended a hagwon last year, according to Korea’s Ministry of Education, Science and Technology, a figure which peaks at close to 87 per cent among pupils aged seven to 13.

The holy grail of many hagwons is securing a place at one of the nation’s top universities, a strategy for which many parents spend years planning in the belief it will guarantee lifelong professional and financial security. The system is not without its critics, though. Students complain of working too hard in a competitive environment and the costs are undoubtedly a burden for some parents. Meanwhile, the government is frequently at loggerheads with these institutions as it attempts to regulate the trade.

On a humid Tuesday evening in the affluent Gangnam district of Seoul, high school students lug their books to the second floor classrooms of Daechi MIT Maths Hagwon. Here, around 120 students from kindergarten age to late teens are tutored daily until 22.00 by hagwon teachers in small groups in intensive maths classes. “There’s a very strong belief among Koreans that you should not bequeath poverty to your children,” says Lee Jeng-sin, school director. “It’s very competitive among students. Parents have been known to spend as much as 10m won [€6,700] a month on hagwon education to get them into a top establishment. A lot of non-verbal pressure comes from their parents. Some children find it very difficult to express their feelings.”

While the parents may be happy to pay, the students aren’t always ecstatic about the extra hours. Among students milling in the corridor is Wee Hye-seung, a 16-year-old girl still in uniform who studies at the hagwon four times a week and admits to sleeping only six hours a night. Looking tired, she says, “I’ve been going to hagwon since I was pretty young. I attend a lot of after-hours’ programmes at my school too. They’re similar to the classes here. I don’t really enjoy either.”

Lee Dong-hyeong, a 16-year-old boy who hopes to study finance at university, says: “Are my friends and I happy? I’m not sure. We’re always tired from studying to be honest.”

But students aren’t just made up of locals: a growing (and affluent) market comprises overseas South Koreans who return to study in the summer holidays in order to gain entry to the country’s top universities, with some schools opening branches abroad to cater to the demand. Recently US students have even started travelling to Seoul for special cram sessions for SAT exams.

“We already have waiting lists for our summer courses for Korean students living abroad,” says Lee. “And there are many schools opening abroad mainly targeting Koreans who live outside the country. It’s a big business.”

Back across the city in the backstreets of Noryangjin – another popular hagwon area – crowds of young children swing brightly coloured school bags as they make their way to classes. Some make a beeline for the Yewon Music Academy, a hagwon where small pink Hello Kitty slippers are lined up neatly in the entrance.

The school is home to a row of half a dozen identical white cubicles, each containing an upright piano and a small child thumping out scales or practising pieces. “We have around 50 to 60 students from the age of about six and most of them come here every day,” says Seo Eun-ji, the piano teacher.

While some practise the piano, others wait their turn in the back room, where young children sit at small yellow desks and quietly do their homework. “These children are extremely busy,” says Seo. “Their parents are mostly working and they normally come here after visiting other hagwon. They’re often very tired.”

Like most hagwon in Seoul, the school has a 22.00 curfew – one of a string of measures that the government has introduced to regulate the industry. And regulation is a big job: there are currently more than 85,000 registered cram schools with more than 10 students in a class, an additional 46,000 specialist classes for smaller groups and over 80,000 private tutors. According to some studies, hagwon represent one of Korea’s top 10 business sectors.

South Korean parents spent on average €14bn on private tutoring in 2008 – nearly double what they did seven years earlier and accounting for about 2 per cent of GDP – according to Korea National Statistical Office figures. Regulations are not without controversy. This July, the law was revised to introduce a raft of measures monitoring hagwon, making it essential to post all fees online and issue receipts, as well as offering cash rewards for whistleblowers. The initiatives, masterminded by the Ministry of Education’s private institute monitoring team, prompted widespread protests among hagwon owners.

In his seventh floor office at the Central Government Complex in Seoul, Ju Myung-hyun, director of the team, defends the measures. “Korea does not have any natural resources,” he says. “Our biggest resources are raising humans. We understand that hagwon have contributed to developing good human beings. We are not against them, nor do we want complete control. But we need these businesses to operate transparently because excessive costs can be a big burden to parents.”

Opposition to the government’s stance, however, remains. One outspoken critic is Park Kyung-sil, chairwoman of the Korea Association of Hagwon and president of the Pagoda Academy hagwon. Sipping tea in her opulent office in the school’s flagship Pagoda Tower, she explains, “The reason there are so many hagwons is due to lack of government investment in education. Korea developed very sharply over 30 years and the government has not invested as fast as the country developed.” Her husband Go In-gyong, Pagoda chairman, adds: “Trying to restrict these hagwon – which are a crucial part of Korea’s education culture – would be a big obstacle to diversity and creativity in the 21st century.”

Regardless of the consequences of the government versus cram school clashes, one certainty remains: hagwon are a vital tool in the nation’s academic successes and are most likely here to stay.