They line up in rows of five as neatly as kindergartners are capable of lining up - 20 of them, dressed in whites and proudly displaying newly acquired white belts.
They bow to the American flag and then to their "master" and begin a half-hour of tae kwon do, a Korean martial art that fulfills the state physical education requirement at Midtown Academy in Bolton Hill.
Twice a week, every child in Midtown's kindergarten through seventh grade squares off in the basement multipurpose room for 30 minutes of punching, kicking, dancing, stretching, aerobics and meditation, sometimes to the recorded accompaniment of monks' chants or New Age music.
At the heart of tae kwon do at Midtown is Mark Seidel, 49, a fourth-degree black belt known around the school as "Master Mark."
Seidel spends the better part of three days a week at the Mount Royal Avenue school, which is in the old Corpus Christi Church school and has limited play space. He also teaches the art - he prefers "art" to "sport" - Wednesday evenings and Saturday mornings for parents and other adults and children who can't participate weekdays.
"Master Mark has played a major role in transforming the school, and because of the discipline he's instilled in these kids, our academics have improved," says Diane Issel, who is in her third year as Midtown director.
She says Seidel "owns a good part" of the school's 12-point gain on the latest round of the state achievement tests, placing it near the Maryland average.
Nearly two years into the program, kindergarten teacher Samantha Calise says: "The kids ... are more highly disciplined, and that rubs off in the classroom. Even though he didn't come here the traditional way, we've learned from him."
Issel says the tae kwon do classes were initiated by parents at the school, one of several in the city that are independently operated but financed as part of the city school system. The tae kwon do classes are paid for by funds raised privately.
Issel says Midtown's independence from city regulations made possible the switch to tae kwon do two years ago.
"We may be the only school in the nation with tae kwon do instead of physical education and a master doing the teaching," says Issel. (The Academy of the Pacific Rim, a charter school near Boston, teaches tai chi, a Chinese form of exercise, during part of the academic year.)
Although tae kwon do teaches self-defense - Julie McClellan says she's happy her kindergarten daughter Rose Woolson, 5, will grow up "being able to take care of herself" - Seidel emphasizes that no one at the school gets a chance to hit anyone except the master.
"They all get a chance to take a whack at me," Seidel says with a smile, "but I don't teach any kid how to fight, and I discourage and deplore violence. We've gotten the wrong idea about martial arts from all of those dreadful movies."
Still, all of the practice punching and kicking eventually makes Jack (or Jill) a powerful boy (or girl), "and because we can't demonstrate the power on each other, we break boards," Seidel says.
Two weeks ago, Midtown held its first belting ceremony of the year. Kindergartners and first-graders got their beginning white belts, while older kids got yellow belts.
Before tying the new belts around each child's waist, the master tapped head and shoulder, saying, "May this belt bring wisdom to your mind and strength to your body."
There's also a spiritual aspect to tae kwon do, to which few parents objected when the program began in 2000.
"We teach that body, mind and spirit should be in harmony," says Seidel, "but don't confuse spiritual with religious. Spiritual is about the inner body."
A typical class goes by quickly. The white-haired master engages in the exercises with his pupils. "The kids give you back exactly what you put in," Seidel says. "They've got to see me sweat."
And sweat he does.
There are old-fashioned calisthenics, including jumping jacks and sit-ups (legs bent, please, to prevent back injury).
There might be 15 minutes of work on kicks and punches, some stretches and low-impact aerobics.
Part of tae kwon do resembles ballet. Kids flap their arms to the song "I Believe I Can Fly," little realizing they're developing muscles to defend against attacks from the side.
The master walks among his pupils, feigning punches and kicks. "Listen to your hand," he says. "Your hand says block." Or "Who's the boss of your body? Your mind tells your body."
Counting in Korean
Exercises are counted in Korean, which Seidel says is the universal language of tae kwon do "in the same way English is the universal language of airline pilots."
Interspersed are periods of meditation. First-graders sit with "eyes gently closed" - Seidel's instruction - while he swings a bamboo stick, stopping an inch from each 6-year-old face. Not a one flinches. "They have to be taught to meditate and to breathe," says Seidel. "Humans are by nature shallow breathers."
It's not always ideal, of course. Kids who act up are invited to take "chill-out time" on the sidelines.
There was a lot of chill-out time when Seidel came to the school in 2000. He'd had no experience in a public school before, and his first attempts to keep order at Midtown were disastrous. "I spent the first couple of months looking for a way out," he acknowledges.