Junior High School 22, in the South Bronx, had run through six principals in just over two years when Shimon Waronker was named the seventh.

On his first visit, in October 2004, he found a police officer arresting a student and calling for backup to handle the swelling crowd. Students roamed the hallways with abandon; in one class of 30, only 5 students had bothered to show up. “It was chaos,� Mr. Waronker recalled. “I was like, this can’t be real.�

Teachers, parents and students at the school, which is mostly Hispanic and black, were equally taken aback by the sight of their new leader: A member of the Chabad-Lubavitch sect of Hasidic Judaism with a beard, a black hat and a velvet yarmulke.

“The talk was, ‘You’re not going to believe who’s running the show,’ � said Lisa DeBonis, now an assistant principal.

At a time when the Bloomberg administration has put principals at the center of its efforts to overhaul schools, making the search for great school leaders more pressing than ever, the tale of Mr. Waronker shows that sometimes, the most unlikely of candidates can produce surprising results.

Despite warnings from some in the school system that Mr. Waronker was a cultural mismatch for a predominantly minority school, he has outlasted his predecessors, and test scores have risen enough to earn J.H.S. 22 an A on its new school report card. The school, once on the city’s list of the 12 most dangerous, has since been removed.

Attendance among the 670 students is above 93 percent, and some of the offerings seem positively elite, like a new French dual-language program, one of only three in the city.

“It’s an entirely different place,� Schools Chancellor Joel I. Klein said in a recent interview. “If I could clone Shimon Waronker, I would do that immediately.�

Not everyone would.

Mr. Waronker has replaced half the school’s teachers, and some of his fiercest critics are teachers who say he interprets healthy dissent as disloyalty and is more concerned with creating flashy new programs than with ensuring they survive. Critics note that the school is far from perfect; it is one of 32 in the city that the state lists as failing and at risk of closing. Even his critics, though, acknowledge the scope of his challenge.

“I don’t agree with a lot of what he’s done, but I actually recognize that he has a beast in front of him,� said Lauren Bassi, a teacher who has since left. “I’m not sure there’s enough money in the world you could pay me to tackle this job.�

Mr. Waronker, 39, a former public school teacher, was in the first graduating class of the New York City Leadership Academy, which Mayor Michael R. Bloomberg created in 2003 to groom promising principal candidates. Considered one of the stars, he was among the last to get a job, as school officials deemed him “not a fit� in a city where the tensions between blacks and Hasidic Jews that erupted in Crown Heights, Brooklyn, in 1991 are not forgotten.

“They just said he may be terrific, but not the right person for that school,� Chancellor Klein said.

Some parents at J.H.S. 22, also called Jordan L. Mott, were suspicious, viewing Mr. Waronker as too much an outsider. In fact, one parent, Angie Vazquez, 37, acknowledged that her upbringing had led her to wonder: “Wow, we’re going to have a Jewish person, what’s going to happen? Are the kids going to have to pay for lunch?�

Ms. Vazquez was won over by Mr. Waronker’s swift response after her daughter was bullied, saying, “I never had no principal tell me, ‘Let’s file a report, let’s call the other student’s parent and have a meeting.’ �

For many students and parents, the real surprise was that like them, Mr. Waronker speaks Spanish; he grew up in South America, the son of a Chilean mother and an American father, and when he moved to Maryland at age 11, he spoke no English.

“I was like, ‘You speak Spanish?’ � recalled Nathalie Reyes, 12, dropping her jaw at the memory.

He also has a background in the military. Mr. Waronker joined R.O.T.C. during college and served on active duty for two years, including six months studying tactical intelligence. After becoming an increasingly observant Jew, he began studying at a yeshiva, thinking he was leaving his military training behind.

“You become a Hasid, you don’t think, ‘Oh my God, I’m going to suppress revolutions,’ � Mr. Waronker said. But, he said, he drew on his military training as he tackled a school where a cluster of girls identifying themselves as Bloods stormed the main office one day looking for a classmate, calling, “We’re going to get you, you Crip.�

He focused relentlessly on hallway patrols, labeling one rowdy passageway the “fall of Saigon.� In an effort to eliminate gang colors, he instituted a student uniform policy.

He even tried to send home the students who flouted it, a violation of city policy that drew television news cameras. In his first year, he suspended so many students that a deputy chancellor whispered in his ear, “You’d better cool it.�

In trying times — when a seventh grader was beaten so badly that he nearly lost his eyesight, when another student’s arm was broken in an attack in the school gym, when the state listed J.H.S. 22 as a failing school — Mr. Waronker gathered his teachers and had them hold hands and pray. Some teachers winced with discomfort.

At first Mr. Waronker worked such long hours that his wife, a lawyer, gently suggested he get a cot at school to save himself the commute from their home in Crown Heights.

He also asked a lot from his teachers, and often they delivered. One longtime teacher, Roy Naraine, said, “I like people who are visionaries.�

Sometimes teachers balked, as when Mr. Waronker asked them to take to rooftops with walkie-talkies before Halloween in 2006. He wanted to avoid a repetition of the previous year’s troubles, when students had been pelted with potatoes and frozen eggs.

“You control the heights, you control the terrain,� he explained.

“I said, if you go on a roof, you’re not covered,� said Jacqueline Williams, the leader of the teachers’ union chapter, referring to teachers’ insurance coverage.

Mr. Waronker has also courted his teachers; one of his first acts as principal was to meet with each individually, inviting them to discuss their perspective and goals. He says he was inspired by a story of how the late Rabbi Menachem Mendel Schneerson, the Lubavitch spiritual leader, met with an Army general, then inquired after his driver.

“That’s leadership,� he said, “when you’re sensitive about the driver.�

Lynne Bourke-Johnson, now an assistant principal, said: “His first question was, ‘Well, how can I help you, Lynne?’ I’m like, ‘Excuse me?’ No principal had ever asked me that.�

The principal enlisted teachers in an effort to “take back the hallways� from students who seemed to have no fear of authority. He enlisted the students, too, by creating a democratically elected student congress.

“It’s just textbook counterinsurgency,� he said. “The first thing you have to do is you have to invite the insurgents into the government.� He added, “I wanted to have influence over the popular kids.�

These days, the congress gathers in Mr. Waronker’s office for leadership lessons. One recent afternoon, two dozen students listened intently as Mr. Waronker played President Franklin D. Roosevelt’s address after the bombing of Pearl Harbor, then opened a discussion on leadership and responsibility.

When an etiquette expert, Lyudmila Bloch, first approached principals about training sessions she runs at a Manhattan restaurant, most declined to send students. Mr. Waronker, who happened to be reading her book, “The Golden Rules of Etiquette at the Plaza,� to his own children (he has six), has since dispatched most of the school for training at a cost of $40 a head.

Flipper Bautista, 10, loved the trip, saying, “It’s this place where you go and eat, and they teach you how to be first-class.�

In a school where many children lack basic reading and math skills, though, such programs are not universally applauded. When Mr. Waronker spent $8,000 in school money to give students a copy of “The Code: The 5 Secrets of Teen Success� and to invite the writer to give a motivational speech, it outraged Marietta Synodis, a teacher who has since left.

“My kids could much better benefit from math workbooks,� Ms. Synodis said.

Mr. Waronker counters that key elements of his leadership are dreaming big and offering children a taste of worlds beyond their own. “Those experiences can be life-transforming,� he said.

So when Emmanuel Bruntson, 14, a cut-up in whom Mr. Waronker saw potential, started getting into fights, he met with him daily and gave him a copy of Jane Austen’s “Emma.�

“I wanted to get him out of his environment so he could see a different world,� Mr. Waronker said.

Mr. Waronker has divided the school into eight academies, a process that has led to some venomous staff meetings, as teachers sparred over who got what resources and which students. The new system has allowed for more personalized environments and pockets of excellence, like an honors program that one parent, Nadine Rosado, whose daughter graduated last year, called “wonderful.�

“It was always said that the children are the ones that run that school,� she said, “so it was very shocking all the changes he put in place, that they actually went along with it.� Students agree, if sometimes grudgingly, that the school is now a different place.

“It’s like they figured out our game,� groused Brian Roman, 15, an eighth grader with a ponytail.

Back in Crown Heights, Mr. Waronker says he occasionally finds himself on the other side of a quizzical look, with his Hasidic neighbors wondering why he is devoting himself to a Bronx public school instead of a Brooklyn yeshiva.

“We’re all connected,� he responds.

Gesturing in his school at a class full of students, he said, “I feel the hand of the Lord here all the time.�