Cheerleaders leaped into the air amid the pop and shower of confetti cannons outside South Philadelphia High on Wednesday. The mayor looked on, clapping.

Students kept looking up at the reason they had gathered in the bitter cold: The new mural that told their school's story — colorful, complex, proud.

"That's me up there," said Rakim Perry, a South Philadelphia senior who has been involved in the project since its inception in 2016. He smiled at Parts Per Million, the giant mural highlighting the school's diversity, which took its inspiration from math, science, and geography.

Southern, as it's known, is an imposing building that takes up an entire city block, South Broad between Snyder and Jackson. Parts of the plain, tan brick facade had been decorated with a mural in years past, but the scenes — a young woman holding an artist's palette, a young man reading — had been neglected, chipped, and faded. It seemed like a marker from another time.

When the new Mural Arts Philadelphia partnership began a few years back, school principal Kimlime Chek-Taylor told artist Ben Volta that she wanted something welcoming for her building, something that told the story of a school where dozens of languages are spoken.

"It's such a big, complex place," said Volta. "It felt like it needed a lot of love, a little bit of color."

Volta first began his work in an algebra classroom with no plan other than to listen to students' thoughts and to help them build something. Students, both longtime Philadelphia residents and English-language learners, worked once a week with Volta and their teachers to dream up a project that would express the school's international energy in languages everyone understood: science and math.

Even kids who felt tentative about their science and math abilities were suddenly engaged once art entered the picture, Volta said.

"Lightbulbs went off," he said.

Project-based learning is in vogue now, but the work done at Southern is the real deal, said Jane Golden, executive director of Mural Arts Philadelphia.

"This was about open-ended questions, collaboration, critical thinking, about giving students a voice. It was about encouraging reflection and revision, encouraging young people to be courageous and fearless," Golden said. "You're seeing something bigger than yourself evolve."

At first, the students connected coordinates. Eventually, they created shapes, drew fractals and spirals, DNA sequences, and satellite orbits. The finished product combines all of these things and incorporates 27 flags, representing each of the languages spoken by Southern students. Students were involved from start to finish, from ideas to painting.

"This new mural is an incredible example of many different academic disciplines coming together to create something beautiful," Mayor Kenney said at the mural dedication ceremony Wednesday. "Parts Per Million shows us that we're all connected."

The mural stretches over the entire front of the building, even underlaying the letters that spell out the school's name.

To Chek-Taylor, the new piece of public art is "bright, lovely — that's what high school should be about, a place that says, 'I want to be here.' "

Janelle Harper, Southern's community schools coordinator and a point person for the project, said the mural is key to telling the community what the school is now. Almost a decade ago, Southern made international headlines when it exploded in racial violence, with dozens of immigrant students assaulted in a daylong series of attacks on Dec. 3, 2009.

Southern still struggles academically, but it has made major strides in climate, becoming one of the city's first community schools — a hub with extra supports and a decided sense of welcome for its 500-plus students, 89 percent of whom live below the poverty line and 20 percent of whom are learning English.

"To me, this just gives the building a new lift," said Harper.

Golden, whose organization works with 2,000 young people annually and is now working on large-scale mural projects at Kensington High and the U School, remembers vividly when Mural Arts began working in Philadelphia schools.

"I remember thinking, 'These kids go to school in places that look like prisons, that look like barracks,' " said Golden. "Our kids deserve to be in beautiful learning environments, and it has so much power if kids can see their thoughts and ideas on a large scale, permanently."