The park behind Benning Terrace, a housing project in Southeast Washington, was once a place where anyone who dared enter risked being shot. The graffiti, said David Gilmore, the receiver of the D.C. Housing Authority, once read: "You are now entering a war zone."

So why were hundreds of kids gathered there amid a sea of red and yellow balloons on Thursday dancing to music? Why had the same young people scurried around earlier to paint houses, plant flowers, help seniors do their spring cleaning and build a brand new playground?

A peaceful revolution is taking place all over the country. It's a revolution against cynicism, despair and selfishness. The celebration in the park at Benning Terrace -- and the hard work that preceded it -- was organized by City Year, a group that has put thousands of teen and twentysomething volunteers into neighborhoods around the country to do simple but fundamental work rebuilding communities, and community.

Ah, middle-class do-goodism, you say dismissively. Nope. A large share of the volunteer force on that sunny day came right out of the neighborhood, kids with a powerful stake in planting, building and painting.

The work of reclaiming Benning Terrace was begun long before by local groups, among them the Alliance of Concerned Men. Many in the alliance are ex-offenders who want to save kids from going the same way.

A couple of years ago, in the very place we were standing, "the kids weren't coming out playing, the women weren't on the street, the elderly weren't sitting on the porches," said Tyrone Parker, a founder of the alliance.

"What you're seeing today is what could occur if you give it the opportunity to happen," he said proudly. "This is an expression of communities coming together, including outside communities, committed to people as a whole -- all different nationalities and races."

Two large forces are at work in the country creating change for the better. One is neighborhood activism. The other is community service, dedicated young people -- many of them receiving modest stipends from the federal government's AmeriCorps program -- willing to spend a year or more making a small piece of the world better.

We praise entrepreneurs these days. Here are social entrepreneurs, some of whom gathered around a wooden table in the park to tell their stories.

Jason Pendrock, 19, works on a City Year project in Philadelphia called the Greater Philadelphia Book Bank. It collects volumes that would otherwise be thrown out or shredded and gives them away. The books go to children, church libraries, teachers who pass them on to students. The group, Pendrock said, has collected and warehoused 2 million volumes. Move over, Amazon.com.

Nobody is too young to serve. Twelve-year-old Edwin Santiago, who goes to the Roberto Clemente Middle School in North Philadelphia, didn't like the condition of his neighborhood. So he joined a City Year project. "We sweep the streets and plant some stuff," he said. "I just felt like helping people and just started to do it."

Nikki Tabron, 22, worked in an after-school program at the Boys and Girls Club in Columbia, S.C., mentoring kids and getting them to do their homework. Caring about somebody actually works. "They know we're proud when they're doing their homework," she said.

And forget about those expensive sensitivity training consultants. You want to heal racial divisions? Get people to work together. "I've seen gang members join the corps," Tabron said, using the Marine terminology City Year volunteers prize, "who didn't like people of different colors." Their racial animosities went away, she said, after a year of labor in a common endeavor.

"There are very few places in America where people come together across racial lines," said Michael Brown, a founder of City Year, and national service is one of those few. Robert Lewis Jr., Boston City Year's executive director, carries memories of a grandfather killed by the Ku Klux Klan. "I wanted to be part of something that united people and didn't divide people."

After the Columbine High School tragedy, said Alan Khazei, City Year's other founder, "the whole country has been wringing its hands about what we should do for young people." The answer, he argues, is already there, and it lies in promoting service.

"Everyone is saying: `What do we do for our children?' " says Brown. "It's time we ask something from our children." What kids crave is responsibility and a sense of power, he says. It is not at all paradoxical that they gain both by serving others.