Several students sit around a conference table at Simon Gratz High School in North Philadelphia on a surly winter’s day, the kind that makes even the school’s drafty classrooms seem welcoming. They are there to give their assessment of the school – and they’re not afraid to be blunt.

“I like this school, but I kind of don’t,” says Chynah Perry, age 15, a thin girl with straight posture and stylish black-rimmed glasses. “It’s strict. Real strict.”

Quaseem Foxwell, a linebacker on the football team, says several of his friends left the school because of the tough rules. Yet he defends the strictures. He says he improved his own behavior after a heart-to-heart with his teachers and administrators. “When I came here and got into a fight, they told me I could get kicked out, or I could talk to the teachers and some of the deans,” he says. “The strict rules are all for a reason.”

All this might be a normal, harmless conversation except for the person sitting a few chairs away listening in, whom the students seem oblivious to: Scott Gordon, chief executive officer of Mastery Charter Schools, the private nonprofit that runs Simon Gratz.

While he may be relatively invisible to the students, Mr. Gordon is hardly unknown outside the school: He has been one of the most revered and reviled figures in the bitter fights over public education in Philadelphia for the past decade, and now he’s starting to wield influence in the school-reform movement nationwide.

As the overseer of 21 charter schools in Philadelphia, he has carved out a reputation as a turnaround artist – someone willing to try to fix high schools that are failing, a task that many other reformers have shied away from in their quest to transform urban education. Indeed, even in the mission-driven charter school movement, reformers often only open high schools they can start from scratch, and then they may only admit students they’ve already indoctrinated with their approach in earlier grades.

Not Gordon. He frequently takes on the worst of the worst – and he’s had some success. As a result, he has become an increasingly important figure in the burgeoning charter school movement. People ranging from former Education Secretary Arne Duncan to Oprah Winfrey have praised what goes on in Mastery’s classrooms. One Mastery teacher calls Gordon an intensely passionate “quiet storm” who “doesn’t feel compelled to put on a big show.”

Yet not everyone is so charitable. Critics accuse him of being an outsider who is dismantling the city’s public schools in an attempt to create a private education empire.

Now Gordon faces his severest test yet. He is shifting his approach in running the schools away from a “no excuses” model that has defined much of the urban charter school movement to a more supportive approach that takes into account students’ backgrounds.

“A mistake that we made was the assumption that schools were not successful because they weren’t well run, or they weren’t well organized, or that teachers weren’t trained and supported,” he says in an interview at Mastery’s headquarters in a wing of a struggling middle school the charter chain took over in 2007. “That may ... be true.” But, he adds, “our communities face lots of barriers and problems – kids in trauma – that need to be addressed if we’re going to be successful.”

The changes under way at Mastery could signal a wider shift in the culture of charter schools and possibly the end of the no-excuses model nationwide. This is especially true as more private operators venture into the difficult territory of school takeovers, driven in part by states such as Tennessee and Nevada that have passed laws encouraging charters to try to resurrect struggling institutions.

But whether Gordon’s latest experiment will catch on across the United States will depend in part on what happens in the hallways and classrooms of Simon Gratz.

Ann Hermes/Staff Maggie Sieleman-Ross (c.), a reading instructor at Simon Gratz, watches the hallway as students change classes.

Built in the 1920s, the giant Gothic school on the border of North Philadelphia’s Nicetown-Tioga neighborhood could be considered one of the enfants terribles of the Philadelphia school system. It has been plagued by violence for years.

More than 40 percent of the school’s 280 freshmen show up reading below a fifth-grade level. Several city special-education programs are located at the school, so about a third of students also have special needs, ranging from cognitive disabilities to emotional disorders. In 2011, the year before Mastery took over, the graduation rate was 58 percent.

Administrators started out by instituting the no-excuses playbook, as Mastery had done at several of its other institutions. Under this approach, students are held to high standards no matter what circumstances they come from – or what happens at home at the end of the school day. The strategies typically include strict discipline, extra time in school, drilling in math and English, and accountability for teachers and principals, usually based on testing. Administrators adopt a rigid set of rules and punishments. A top-down lecturing style is followed in the classroom.

At Simon Gratz, students began raising their hands in class, tucking in their shirts, and racking up demerits and detentions for the smallest infractions.

The new administrators also dismantled the metal detectors guarding the entrance of the building. The idea was to make it seem more like a scholarly institution and less like a prison. But in this case students and parents balked. They didn’t feel safe without the detectors, security guards, and bag checks. The school, nevertheless, came off the state’s “persistently dangerous” list as the hallways calmed down and fewer fights broke out.

Teachers drilled students in note-taking strategies and the standards they had to master. Test scores rose at first. But then they stalled. Simon Gratz still wasn’t the friendly, dynamic place Mastery administrators had imagined.

The high expectations and rigid rules weren’t enough to erase the trauma that has scarred many kids. In the years after Mastery took over Simon Gratz, one student witnessed her father shoot and kill her mother. Another saw his uncle shot in the head and had to drag his best friend’s body to a police car after he was gunned down in the street. An honors student was hit by a stray bullet and died. Another student accidentally shot himself.

Gordon worried that Mastery was in danger of confirming what many critics often charge about charter schools: that while many of them may do a good job of preparing kids to do well on standardized tests and get into college, their students founder once they arrive on campus. That the mostly white leaders of urban charter networks are, at best, out of touch with the mostly black and Hispanic communities they serve, or, at worst, guilty of a paternalistic racism that undermines their mission of uplift.

Gordon was ready to make a change. “We were frustrated that we couldn’t break through,” he says. “We got feedback from our graduates that the ... support structure that we had created for students – ‘kids will not fail’ – was not serving them once they got into the real world. The real world was not as supportive. They had to really develop the independence to manage themselves.”

Gordon tinkered with parts of the model, but after struggling to get it right, he decided to start over. Mastery administrators introduced a new curriculum, new teaching methods, and a new disciplinary system. They hired more social workers and brought in more assistance from community organizations that help kids deal with trauma. They made training in racism and “cultural context” mandatory for all of Mastery’s teachers and administrators, across every school in the city.

“Often you see people who are really bold as those who might not listen,” says Kathy Hamel, a partner at the Charter School Growth Fund, a nonprofit that supports Mastery. “But [Gordon] is a very good listener, and he’s learned to listen and adapt.”

Mastery administrators decided that to serve their students best, they should make sure all had the option to go to college, but not insist on it. They began developing programs to support students headed into the military or to technical programs and immediate jobs. Even the charter network’s motto – “Excellence. No Excuses.” – is under review.

“We still believe there are no excuses for this country not to be able to provide a great education for every kid,” Gordon says. “There is no excuse; every child can learn and be successful. But I’m not sure it speaks to the soul of Mastery right now. That’s part of our job: to prepare our kids for the real world, and to recognize that there’s great promise in the world. It’s also a broken world.”

Ann Hermes/Staff Mastery CEO Scott Gordon, talking to a middle school student, is changing the way his nonprofit runs its charter schools in Philadelphia.

Gordon’s own life straddles different worlds. The trim, soft-spoken administrator wears ties and no suit jacket to work. He lives in an upscale Philadelphia neighborhood, Chestnut Hill, but drives a 2007 Prius. He is criticized because his own children, two boys ages 13 and 15, don’t attend Mastery schools. One goes to a public magnet school, and the other a private Quaker school. He says he urged them to try a Mastery charter, but didn’t push them when they said “no.”

His route to becoming a school magnate was circuitous. Raised partly in Philadelphia by parents who were both teachers, Gordon worked as a street vendor selling health food and as a substitute teacher before heading off to get his Master of Business Administration at Yale University in New Haven, Conn.

“I thought the way to change the world was to start businesses that provided employment opportunities for poor folks,” he says.

After graduate school, he worked at a welfare-to-work business for home health-care aides in the Bronx, a borough of New York City, and then replicated it in Philadelphia. The mostly black and Hispanic aides and nursing assistants were co-owners in his company. He trained the women and helped them go back to school for their nursing degrees, but many stumbled with the basic academic skills. “I saw the consequences of families and children not getting what they need from the education system,” Gordon says.

In 2000, a series of events pushed him toward education. The son of one of the women he worked with, a young man who had dropped out of high school, was shot in the street and paralyzed. Gordon’s mother, who taught special education in a suburban town outside Camden, N.J., died unexpectedly. And his first son was born.

He initially looked into becoming a teacher or principal. “It was hard to get a job because I didn’t have a traditional background, wasn’t certified,” he says. “What I had to offer was management skills.” So he teamed up with a veteran educator, Deborah Stern. Their first charter, Lenfest, opened in Philadelphia in 2001. The high school was modeled on a progressive San Diego school, High Tech High, where students learn by doing projects: creating a bike tour to learn about the city or studying physics by making surfboards. The school culture was “student-led,” Gordon says.

But he and Ms. Stern discovered their students didn’t have strong enough academic backgrounds to succeed in the loosely structured project-based curriculum. They pivoted to the no-excuses model, switching from projects to direct instruction – in which teachers lecture, students listen.

It worked. Mastery’s schools began outperforming most of the other schools in the city as the network expanded with both completely new charters and turnarounds it took over under a city program to revitalize struggling schools.

To Gordon’s critics, success came at a high cost. Mastery replaced scores of teachers as it took over district schools, and the strict discipline codes drove some students away – back into floundering neighborhood schools with the neediest students. The rapid growth of charter schools in Philadelphia has siphoned away money from an already impoverished city school district forced to shutter schools and lay off staff. A 2014 article in the liberal publication The Nation headlined a story on Mastery’s rapid expansion “How to Destroy a Public-School System.”

“There seems to be a political and financial will to help them [charter schools] succeed, and our schools were being closed,” says Stephen Flemming, who teaches third grade at John B. Kelly Elementary School. In his classroom, he says, “we have one desktop computer.”

Gordon says Mastery’s focus on taking over existing schools means his charter network has had a much smaller effect on the district’s finances. But takeovers are often politically fraught, and local communities have not always welcomed Mastery. Kendra Brooks, a mother of four, organized against Mastery’s efforts to run the Edward T. Steel elementary school a few blocks from Simon Gratz.

“The narrative that the school was failing, the teachers were failing – it wasn’t telling the whole story,” Ms. Brooks says. “Before the state budget cuts, we were doing just fine.” She says the district added three grades and cut staff in response to budget reductions, sending the school into decline.

“We were happy with the teachers we had,” she adds. And she was not impressed with Mastery, which she believed cherry-picked only their best data as they pitched themselves to parents.

In May 2014, Steel parents voted overwhelmingly against the Mastery takeover of their school. Yet even some regular critics of the local charter sector have praised Mastery’s takeover work.

“The thing that stands out to me is their willingness to do school turnarounds, as opposed to a lot of other charter operators who want to expand big time and want to do it on their own terms,” says David Lapp, a lawyer at the Education Law Center in Philadelphia, which has sought to curb charter expansion. “Mastery serves a much more needy student population than most charter operators in Philadelphia, to their credit.”

Mr. Lapp is also encouraged by the shift to a more progressive vision. “I think it’s a testament,” he says, “that they’re willing to try.”

Ann Hermes/Staff Isaiah Sorrell (r.) operates the metal detectors at the entrance to Simon Gratz High School (left). The charter school operator removed the metal detectors when it first took over management of Simon Gratz in 2011. But the nonprofit reinstalled them after parents and students raised concerns.

The sun pours through the tall windows in Maggie Sieleman-Ross’s reading intervention class at Simon Gratz, where ninth- and 10th-graders in blue and khaki uniforms are reading a book about animal scat. The mood is friendly, but serious, and none of the kids crack a grin as she asks a student to explain what “scat” is.

“I guess, poop?” one says.

The teacher turns to another student who had left class early the day before to get his arm checked out after a mishap in gym class. He’s now wearing a cast. “Abdul, my love, I know you had to leave, so you’re going to start at the beginning,” says Ms. Sieleman-Ross. She listens as he reads aloud and stumbles at “examine.”

“What do you think it means?”

“Exam, that’s a test,” he says.

“When you’re reading something and something doesn’t sound right, what do you need to do?” she asks.

“Go back.”

“That’s right, sweetie.”

At Simon Gratz, a third of incoming freshmen spend time each day in classrooms like this; they work in small groups and on computers to get help catching up in reading and math. In these special classrooms and in regular courses, the theme is what Mastery educators call “structured struggle.” They’ve replaced standard lessons with more challenging ones. A teacher will hand out a difficult text for students to read, then talk about strategies to figure it out.

Classrooms and hallways are still orderly, but suspension is now a last resort. Mastery instead uses “restorative practices,” in which students talk out conflicts, and “trauma-informed” discipline, which recognizes that bad behavior can stem from deeper issues, such as violence at home, that the school should help address.

The percentage of students placed in Mastery’s Wayne Academy, an alternative disciplinary program, has dropped from 4.5 percent in 2014 to 2.4 percent today. At Simon Gratz, it’s declined from 9 percent to 3.4 percent, according to data provided by the network. School suspensions have also dropped significantly. Simon Gratz has cut its rate in half, with students now receiving an average of a half-day suspension per year, versus a full day in 2014.

Race is a constant topic of conversation in the schools. A series of workshops has pushed students, teachers, and administrators to consider how identity and culture affect their interactions and biases. Teachers and principals say the training has led to a subtle but significant shift in how Mastery educators see their work.

“A lot of charters come in and say, ‘How can we fix this community?’ ” says Nadia Bennett, principal of Simon Gratz’s upper school. “Mastery says, ‘How can we support you with what you’ve already got going on?’ ”

Even as the network shifts its vision to “Mastery 3.0,” Gordon says one strategy has remained constant: recruiting and developing good teachers. In the past, that meant relying on large numbers of altruistic young rookies – often white – supported by a legion of more experienced coaches and administrators. With Mastery 3.0, there’s more of an effort to bring in teachers from neighborhoods the schools serve. “We need to get more kids from the community teaching at Mastery,” Gordon says. “We need to get more folks of color in the teaching profession.”

It’s still unclear if Mastery’s new approach will lead to better academic outcomes, or undercut the network’s progress. “They’re taking a big risk by trying to take this to the next level,” says Joe Siedlecki, a program officer at the Michael & Susan Dell Foundation, which has provided funding to the Mastery network.

Results so far are mixed. The number of Simon Gratz students graduating has increased 30 percentage points since the takeover, to 89 percent. But test scores dropped last year, as they did across Pennsylvania when the state rolled out new exams aligned to the Common Core standards.

Gordon says he doesn’t just blame the tests for the declines. But he stands by his strategy. “We still think it’s the right thing to do by kids and ultimately will result in greater and deeper math [and reading] achievement for our students,” he wrote in an e-mail. “It’s not a short-term game, though.”

DawnLynne Kacer, executive director of the Philadelphia school district’s charter office, says other charters are considering changes, although few are as far along as Mastery. She says reformers will be watching Mastery to see, “Does the pendulum swing too far in the other direction?”

This year, Mastery fought to take over another Philadelphia school, John Wister Elementary. The city’s School Reform Commission reversed a decision by the superintendent, who advised keeping Wister in the regular public system because test scores had improved in the past year. Anna Figueroa, who has four grandchildren there, is excited about the decision after visiting a Mastery school across town. “It blew my mind,” she says. “We’re going to have a better future for our children’s education.”

But Brooks, now an instructor for the International Institute for Restorative Practices and a member of a local advocacy group that has fought Mastery’s expansion, says the takeover will be a loss for the neighborhood. “Instead of saying, ‘We know what you want. We’re going to come in here and make it all better for all you poor ignorant parents in Philadelphia’ – and I think that’s how they come across,” she says, “we want someone to work with us, and respect us in this process, and build what we want for our community and our children.”

Gordon probably wouldn’t disagree. To him, connecting with the families and communities is just as important as how the students perform on tests. “If we’re going to be successful, what Mastery represents has to resonate with kids and with families,” he says. “We have more work to do.”

This story was produced by The Hechinger Report, a nonprofit, independent news organization focused on inequality and innovation in education.