THOUSAND OAKS, Calif. — The country’s fastest high school distance runners were circling the track on a recent weeknight as Andrew Young dangled from the back of a speeding golf cart with his camera. Young’s twin sons, Lex and Leo, whose YouTube channel has nearly 13,000 followers, had enlisted their father to video their team’s workout for posterity. The problem was they kept outrunning the golf cart.

“I could almost keep up with them on the straightaway,” Andrew Young said.

That might sound familiar to runners who compete against the boys’ track and field team at Newbury Park High School, which is about 50 miles northwest of Los Angeles.

It is no small thing for a public high school to produce one of the best milers in the country. Newbury Park has four of them, including Colin Sahlman, a senior who last month became just the 13th U.S. high school runner to break the four-minute barrier for the mile. Sahlman, 18, said he was glad he reached the milestone ahead of his younger brother, Aaron, and Lex and Leo Young, all of whom are juniors. Colin Sahlman does not think his teammates will be far behind.

“If we could have all four guys under four minutes, that would be insane,” he said.

On Saturday, Newbury Park’s star runners will compete in the four-by-mile relay at the New Balance Nationals Indoor championships at the Armory in Upper Manhattan. Sean Brosnan, the team’s coach, predicted a time of around 16 minutes 20 seconds — an average of 4:05 per mile — which would demolish the national high school record by about 40 seconds.

“Magic could happen,” Brosnan said. “We don’t set boundaries.”

The team is getting a crash course in celebrity. Opposing runners ask for selfies and autographs at meets. Colin Sahlman is in a Gatorade commercial — “I get texts from friends and family who are like, ‘We just saw you on TV!’” he said — while every week or so, Lex and Leo Young post an entertaining glimpse of their lives on their YouTube channel. A recent episode was titled, “What Lex Young Eats on Race Day.” Spoiler: oatmeal for breakfast and a toasted bagel with ham and turkey for lunch.

“Almost halfway through the bagel now,” he says between bites.

With success, though, have come questions: How did this happen? How is it even possible? When a team routinely does things that defy belief, the compliments can start to sound like veiled critiques, and Brosnan acknowledged his skeptics.

“There’s always someone trying to take us down,” he said.

‘They Saw That It Was Possible’

While growing up on Long Island, Brosnan said, he was the type of athlete who devoured track and field magazines. He competed in N.C.A.A. Division II and the N.A.I.A. in college, then ran professionally before he got into coaching. Newbury Park High School hired him as its boys’ distance and cross-country coach in 2016, and he began coaching the girls’ team the next year.

He did not inherit a powerhouse. Newbury Park had not won a league title in about 20 years, he said. Brash, confident and full of youthful energy, Brosnan had all sorts of novel ideas — about hydration, sleep patterns, training. But his first months were challenging. After watching his runners goof off in practice, he would complain to his wife, Tanya: They just don’t care. “I almost quit 10 times,” he said.

It took one athlete to change the dynamic — Ethan Duffy, who began to hold his teammates accountable. His presence, Brosnan said, made a big difference.

If Duffy helped form the foundation, it was Nico Young — Lex and Leo’s older brother — who took Brosnan’s vision and boosted Newbury Park’s stature. A two-time state cross-country champion, Nico Young set several national high school records. Last summer, after his freshman year at Northern Arizona, he placed ninth in the 5,000 meters at the U.S. Olympic trials. Many of his records are now in jeopardy.

“Right now, Colin’s getting his swing at them,” Leo Young said. “But next year, it’ll be Aaron trying to defend the Sahlman name versus Lex and I trying to take some back for the Youngs.”

Brosnan explained part of his approach by citing one of history’s most celebrated runners: Roger Bannister, who, in 1954, was the first person to eclipse the four-minute barrier for the mile. It was an achievement that had seemed incomprehensible. But in the months and years afterward, a host of other men joined him.

“They saw that it was possible, and I think that’s what’s happening with these guys,” Brosnan said, referring to his own athletes. “We’ve created this culture where I have three or four guys who do not think four minutes flat is fast for the mile. One of them already broke it. And we’ll probably have more break it this year. That’s the approach you need.”

Newbury Park flexed its slow-twitch muscle fibers in the fall cross-country season. At the California state meet, the Sahlman and Young brothers swept the top four spots, while Daniel Appleford, a senior, finished seventh. One week later, Colin Sahlman led the team to a second consecutive national title by placing first overall, covering the five-kilometer course in 14:03.29, as Leo and Lex Young took second and third. All three runners broke the national high school record for a five-kilometer cross-country course, which Dathan Ritzenhein, a future Olympian, had set in 2000.

Not to be overlooked: Sam McDonnell, a senior who led the girls’ team to a runner-up result at the state meet, placed sixth at nationals.

“We don’t limit ourselves,” Leo Young said. “It’s the mentality that if you work as hard as you can, then you can trust in yourself to put everything out there.”

Training Hard Under Scrutiny

Last year, Brosnan said, coaches and parents from opposing schools lodged 14 complaints against him and his program with the California Interscholastic Federation, known as the C.I.F., which is the state’s governing body for high school sports. Brosnan rattled off some of the supposed infractions, like organizing a workout on a race day — “They were doing a cool-down run,” he said — and practicing on a Sunday, which is also against the rules. He and his wife, he said, had bumped into a couple of members of the team at a park.

“They say hello and chat for a little bit,” said Steve Hawkins, an assistant coach. “Someone was hiding behind the bathroom taking pictures of them.”

A spokesman for the C.I.F. said the organization does not comment on accusations or complaints involving member schools.

Some people, Brosnan said, seem mad at him for building a dominant program. Mad at him for limiting the number of races that his runners enter. Mad at him for staging his own meets with paid pacers after he determined that too many high school meets were poorly organized. Mad at him for other stuff, which he says is fiction.

“I’ve heard coaches say we recruit,” he said. “I’ve heard coaches say that we run 90 miles a week. I’ve even heard the drug thing, which really upsets me. You know what? That’s super insulting to the kids and their parents. Come on. We’re just running. We work hard.”

No one is doping, Brosnan said, and no one is doing excessive mileage. These are teenagers, after all, and there is a long and fraught history of young runners who have succumbed to injury and burnout. Lex Young said he seldom ran more than eight miles a week entering high school, and now maxes out at around 60.

“Sean really believes in the quality of the miles,” he said. “He’d rather be specific about how those miles benefit you rather than just have you do more.”

At the same time, Brosnan emphasizes recovery and preventive care. He prescribes at least eight hours of sleep. Most of his runners are in bed before 9 p.m.

“Every two days during cross-country season,” Brosnan said, “I’d ask them: ‘How much sleep did you get last night? Seven hours? What are you doing? That’s not enough.’”

He encourages them to consume copious amounts of water — his runners are easily identifiable by the 64-ounce jugs they lug around — and to seek out sports psychologists and massage therapists. Three times a week, they gather before school at 6 a.m. for an hour of stretching and strength training. Before hard workouts, Brosnan sometimes uses a device to measure their hemoglobin, a protein in red blood cells that doubles as an indicator of aerobic capacity. A couple of years ago, he spent about $4,000 on Normatec compression sleeves that are designed to aid recovery, though the team has since discovered some of the benefits of stardom.

“We’re fortunate now that companies give us stuff,” Brosnan said.

Of course, there is no substitute for actual running. Newbury Park’s buildup for the school year starts in the summer, when the program’s top boys and girls head to Big Bear Lake for a month of high-altitude training.

“You wouldn’t sacrifice a month of your summer to spend all that time in a cabin in the woods, running and hanging out with your team and coach, if you didn’t really enjoy it,” Leo Young said.

When Newbury Park hits the track for workouts, the team runs with purpose. Last week, in a tuneup for their meet at the Armory, Brosnan’s fastest runners did a series of intervals: 800 meters in 1:59, then back-to-back 400-meter loops in 59 seconds with one minute of rest between each. After a short rest, they did it all again.

“If you want to run sub-four, you have to run fast,” Brosnan said. “You have to say: ‘We’re going after it. This is a workout, and you need to go hard.’ I don’t know why people don’t want to do that.”

After the workout, Leo Young commandeered the camera from his father so he could video Colin Sahlman pretending to cross the finish line a couple of times, his index finger raised high in the air. It looked as if he had done it before.