On Thursday, hundreds of thousands of students in South Korea will sit for Suneung, an entrance exam that will determine which university they get into.

The annual College Scholastic Ability Test (CSAT), one of the most gruelling moments of a student's life, involves them being tested on Korean, English, maths, social studies and sciences.

Students are graded on the percentage of correct answers in every subject and results are classified in nine categories.

The results have an effect on various aspects of a student's life, including job prospects and marriage.

On the day, offices open late to keep the roads clear for students on their way to the exam, and air traffic is halted during the listening part.

Officials work towards reducing traffic jams and, in some cases, students are also escorted to the examination centres by police officers.

Families offer special prayers at churches and temples for the children.

But what is it like for students to prepare for the exam and sit through it?

Al Jazeera spoke to 19-year-old Lee Yeon-soo, who took the test two years ago, on what a student goes through while preparing for CSAT and sitting through it:

"This single exam will determine your life, basically.

"We study for this exam from the moment we enter grade school. That's 12 years of studying and doing well in Suneung being the end goal.

"The day I became a senior in high school, I wrote '365 days till D-Day' on my calendar and started counting down the days.

"On the day, you're not supposed to eat anything heavy that might affect your performance. I think I ate porridge only.

"Usually, one of your parents will take you to school. At the gates, the teachers and younger students will be waiting for you, cheering, holding up signs and giving out chocolate or candy.

"The fact that your parents and teachers are cheering for you puts you under more pressure. You feel like you have to do well so you don't disappoint them."

'Rough and exhausting'

"You go into the assigned classroom and wait. There is so much tension in these classrooms. Once the exam starts, it goes by really quickly and you don't even know what's happening half the time.

"You take the test for one subject and as soon as that's over, you're onto the next subject. You have lunch and then you immediately jump into the next subject.

"It was really rough and exhausting. I just wanted it to be over.

"Because flights don't take off during the listening test, and the work hours are changed so there's no traffic on the road when we go to school, it feels like the entire country is changing its schedule for this exam. That in itself is huge pressure.

"Most students do worse on the actual exam than the practice ones because there is so much pressure. Even students who did well on the practice tests will do badly on the day because of the nerves involved.

"The exam determines your future. If you don't do well on the exam, students will study one more year to take the test again in the next year. Approximately 20 percent will retake it. Some even take it three times.

"There's even a name for it: Jaesoosaeng is for students who took it twice and Samsoosaeng for those who sat for it three times. A bit of shame comes with those titles.

"When the exam is done, you feel like you've lost direction. It really feels like the end of a huge chapter in your life. I really felt like I had lost my way when I was done with the exam.

"Here was something I had been running towards for the last 12 years of my life, and I was suddenly there. What next?

"The evening after you take the exam, the answers are available online. So you go through them and get a vague idea of how well you did.

"Some students don't come to school the next day because they know they've gotten a bad score. There are also students who start studying for the next year's exam right away. The school feels all over the place basically. You feel really lost."

The 'busy' disease

"Korean high school students are studying all the time.

"From 8am to noon, we have the first set of classes. Then we have lunch. Then we go have classes again until 5pm. Then it's dinner time.

"From 6pm to 10pm, we have after-school study sessions. We review what we learned that day and study for what we're going to learn the next day.

"On the weekends, some of us have tuition. Some people go to five or six sessions. The government has made this law that the tuition centres should close by 10pm, but some still break the law and lock the doors after 10pm, but have university prep classes until 2am.

"I feel like Koreans have a disease. The 'busy' disease. Students are busy studying all the time. They don't have a life away from studies. Schools have become a prison. I think this is a characteristic of being a Korean. It's like this for adults who work, too.

"I took this exam two years ago but if you told me to go back and take it again, I don't think I could. The pressure was immense and I was studying as if I was a machine.

"Now that I'm an adult, I have freedom. I can do what I want to do with my time. The fact that my time is mine to spend, this is something new to me."