Online classes, far cheaper than cram schools, have become a standard part of education expenses for parents, who also usually hire private tutors and enrol their children in cram school.

Critics say the system is geared toward passing the entrance exams, which means students have few analytical skills. In exam subject such as English, students are much better at answering written questions about grammar than speaking the language.

The pressure-packed education system is also blamed for making South Korea have the lowest birthrate in the developed world. It has led some to simply opt out, with fathers, typically the breadwinners, living cheaply in South Korea to pay the costs of sending the children, mothers in tow, overseas for education.

"These late night classes ... can lead to various problems, including a lack of sleep that decreases the effectiveness of learning while raising issues of mental health," said Woo Ok Yeong from Health Education Forum, a child advocacy group.

In her miniskirt, boots and fashionable tops, Rose Lee looks more like a university student, but she's actually one of the country's highest paid English teachers.

Calling herself the "Queen of English" but who asked to be interviewed in Korean, Lee expects to make more than US$7 million a year mostly through online classes. She also works offline, which in the cram school trade means teaching students in a classroom.

"Due to the lack of resources in our country, parents have always felt that education was the best thing they could provide for their children," Ms Lee said through a translator.

Ms Lee has not had much time to enjoy her wealth and knows that her fortunes can easily change in a world where she is dependent on the approval of fickle teenagers.

"I guess the parties will have to come after my retirement."