new middle schools have been coed, and some previously same-sex schools have converted to coed as well. Some schools have converted to same-sex due to pressure from parents who thought that their children would study better in single-sex education. As with primary schools, students pass from grade to grade regardless of knowledge or academic achievement, the result being that classes often have students of vastly different abilities learning the same subject material together. In the final year of middle school examination scores become very important for top students hoping to gain entrance into top high schools, and for those in the middle hoping to get into an academic rather than a technical or vocational high school. Otherwise, examinations and marks only matter insofar as living up to a self-enforced concept of position in the school ranking system. There are some standardized examinations for certain subjects, and teachers of academic subjects are expected to follow approved textbooks, but generally middle school teachers have more flexibility over curricula and methods than teachers in high school. More than 95% of middle school students also attend privately run, for-profit, after-school tutoring agencies known as hagwon (학원), or "cram schools", in order to receive extra instruction from private tutors. The core subjects, especially the cumulative subjects of Korean, English, and math, receive the most emphasis. Some hagwon specialize in just one subject, while others offer all core subjects, constituting a second round of schooling every day for their pupils. Indeed, some parents place more stress on their children's hagwon studies than their public school studies. Additionally, many students attend academies for things such as martial arts or music. Thus, many middle school students, like their high school counterparts, return from a day of schooling well after sunset. The average South Korean family spends 20% percent of its income on after-hours cram schools, more spending per capita on private tutoring than any other country. High school High schools in South Korea teach students for three years, from first grade (age 15–16) to third grade (age 17–18), and students commonly graduate at age 17 or 18. High school students are commonly expected to study increasingly long hours each year moving toward graduation, to become competitive and enter extremely attractive universities in Korea. Many high school students wake and leave home in the morning at 5am. When the school is over at 4pm, they usually go to a