There are at least 50 of them, crowded into a low-ceilinged room with mirrors on three walls. It is hot, it is sweaty and it is 9.30 p.m. on a Wednesday night.
The group, who have been practicing the same move repeatedly for nearly two hours straight, are all students of Def Dance, an elite dancing and singing school in Seoul's upscale Gangnam neighborhood.
"I spend about three hours here every day after school," says Lee Jae-Gi, a skinny 16-year-old wearing a gray sweatshirt. I started taking classes when I was 11."
He studies K-pop, hip-hop and singing. "Practicing the same move over and over again can be tiring but I am progressing and that is all I care about," he adds.
The teenagers enrolled in Def Dance are all single-mindedly pursuing the same aim: to become a K-pop idol
. Becoming one of the chosen few guarantees fame, success and a bank balance that sets them up for life.
But the school, which charges $200 per month and has 1,400 students, some as young as eight, is only the first rung on the ladder to fame.
To become a true idol, teenagers like Lee must first make it through ultra-competitive auditions held by the record labels. Those who are chosen become "trainees." They will be expected to give up their freedom to live and train for several years at one of Korea's elite K-pop academies. Only then will they get a shot at stardom.
There are dozens of schools helping to prep kids for these auditions across Seoul, each charging anything up to $1,000 per semester.
Life as a trainee
Three record labels dominate the K-pop industry, which generated $4.7 billion dollars in 2016, SM Entertainment, JYP Entertainment and YG Entertainment. All were formed in the late 1990s, when K-pop first started to take off.
Their trainee selection process is incredibly competitive. "We hold 500,000 auditions a year," explains Choi Jinyoung, who is setting up a new academy for SM Entertainment. "Less than 10 people get chosen every year to become trainees."
Personality and a "good character," which means being hard-working and disciplined, are the key elements recruiters look for.
Dedication though is no guarantee of success. "Knowing how to dance and sing are not so important," details Patty Ahn, an expert on contemporary Korean culture at the University of California, San Diego. "That can be taught."
Looks -- a crucial element of the K-pop universe, which churns out about 20 new bands every year with perfect faces and figures -- can also be arranged. Most idols have had some form of plastic surgery, says Ahn.
Academy trainees are usually aged between 10 and 14 and spend two to three years following a grueling full-time training schedule, modeled on Korea's military service.
Close to the country's border with North Korea is the Global K Academy.