Chicago schools have wrestled with how to stop youth violence in the city. The school district is spending $60 million dollars over two years to mentor kids and create a “culture of calm.” Fights are a daily occurrence in many Chicago high schools. But one school in a tough neighborhood on the city’s West Side is celebrating a victory: 153 days of peace.

Tens of thousands of city high school students start the school day by going through a metal detector and having security guards check their backpacks for guns or knives.

Contrast that to North Lawndale College Prep: no metal detectors, no burly security guards just inside the front door.

Instead, a couple of teachers are playing catch outside.

Nice catch, good throw…hurry up!

They chase after giggling students, who race to get in the front door before being tagged.

We’ve gotta get her! Yes! Out! Good morning, Keona.

To school founder John Horan, treating kids like they’re not coming to Cook County Jail is part of the recipe for a peaceful school.

Horan has been working at this for years, but this year, the school set a big goal: 90 percent of school days with no fights or physical violence, the equivalent of an “A” in PEACE. Last week, they made it—153 days.

HORAN: We’re able to teach literacy and numeracy—we can teach the skills of peace. This ought to be as important as ACT scores or all these other metrics.

Students and staff here study—really study—Martin Luther King’s principles of nonviolence. They talk about creating what King called the “beloved community.” That might sound like a difficult thing to get teenagers to buy into. Senior Darlisa Scott says it’s not.

SCOTT: Nine out of ten times people don’t want to fight. They just have a reputation to fight because of how they’re raised, or they just want to get their point across.

Scott is what the school calls a “peace warrior.” She and other students have been trained in how to break up fights and keep arguments from escalating.

If a fight does break out, Latrell Hassel is another student who will do something about it. If you meet Latrell, you’re glad he’s for peace. He’s about 6’5”, a lot of pounds.

HASSEL: … an NFL linebacker almost. So with me it’s more like—I don’t want to say intimidation, but um…I guess it’s easier for me to stand in the middle of a fight and just separate everybody. Sometimes it gets dangerous because some people like to just swing all wild, and you might get hit, but you have to focus on the goal of separating the fight.

This is not how students talk at most tough high schools. Many kids in neighborhoods like this one feel they have no choice but to fight—lest they be viewed as weak, and then face the prospect of even more fights. Here, teachers are pounding into kids a different idea of what it means to be strong.

CHILDRESS: Nonviolence is not apathy or being a pushover. We teach students that you resist violence and you resist wrongdoing. You resist injustice, but you do it in a nonviolent way.

Science teacher Tiffany Childress is North Lawndale‘s “peace guru.” She’s reminded daily why this work matters: one of her students attends class in a wheelchair. He was paralyzed by a bullet.

Childress teaches King’s principles of nonviolence. For instance, Principle 1: Nonviolence is a way of life for courageous people. Or Principle 4: Suffering can educate and transform. Shortly after she began the lessons, she started getting text messages from students.

CHILDRESS: A basketball player told me that he was going over a principle in his head because he almost got in a fight on the court—and he didn’t get in a fight because he said he kept saying the principle over and over in his head. And then another young woman, she sent me a Facebook message: ‘Hey, Principle 2 has really been helping me out because this, this and this happened at home.’

Teachers say this is working because peace is part of the school’s very identity; the philosophy is shared by all teachers. Spanish teacher Katie Bordner says students are beginning to enforce norms themselves.

BORDNER: One time when there was a fight in December, I saw students like, ‘Who’s breaking our peace? Why are you breaking our peace?’ They see the fight and they equate it to the breaking of peace, not just the drama and the he-say, she-say things.

The rules here are that any physical aggression breaks the peace—a push, a shove. When students fought at a nearby McDonald’s, that broke the peace too.

This year, the campus cut its fights in half. But there have been struggles to get to 153 days of peace. Sophomore Deshanique Chaney couldn’t help herself last March when she hauled off on a classmate who punched her. He was mad because she was singing in class.

CHANEY: And, you know, we lost the peace day, and everybody was mad because we was trying to gain our peace days. So like, when I did lose that peace day, I felt bad. But after that I ain’t got into no more trouble, and I keep the peace, and I keep other people from fighting.

Kids who mess up have to apologize to their teachers and classmates over the P.A. system, or in an assembly.

Critics often allege charter schools like North Lawndale have an easier time at creating positive school cultures because they transfer problem kids back to neighborhood schools. Administrators here admit some students have left, but they insist they don’t give up on anyone.

North Lawndale students held a parade and rally to celebrate their “A” in peace. Complete with drum corps and dance line, students marched through their poverty-stricken neighborhood holding signs, neighbors cheering them on from cars and third-floor windows.

At a block party that followed, senior Jermaine Winfield stood in a circle of tough-looking guys. One wore a memorial T-shirt, R.I.P. written below the smiling face of his dead friend. You might think this group of kids would have a more jaded view of North Lawndale‘s efforts. Instead, Jermaine says proudly he hasn’t been in a fight all year. And he thinks the school could even make a difference in the neighborhood.

WINFIELD: It’s just like gonna take an effect. Once they see us doing it, everybody else is gonna get to doin’ it. It’s spreading slowly, but it’s gonna get there.

The school is thinking of raising the bar next year—to address verbal violence as well. And students will try again to earn an “A” in peace.