U.S. first lady Michelle Obama rides in a swing while helping to construct a playground at the Imagine Southeast Public Charter Elementary School June 15, 2011 in Washington, DC.

*First lady Michelle Obama mixed and poured concrete, attached swings to a swing set and raked mulch for an hour Wednesday at a charter school in a low-income Southeast Washington neighborhood, helping volunteers to build a new playground from scratch.

The first lady was the guest of honor as KaBOOM!, a nonprofit that gives children opportunities for unstructured outdoor play, constructed the 2,000th playground in its 15-year history.

“This is a very cool experience,” said FLOTUS. “It really is a source of pride to be here today to celebrate the 2,000th build.”

Michelle Obama pushes a fellow volunteer in a swing

The first lady is an advocate for exercise and healthy eating and worked with KaBOOM! before President Barack Obama was elected. It was the second time she has joined the group to build a playground.

KaBOOM! advocates for play as a critical part of children’s physical, intellectual and emotional development. The group works primarily in low-income neighborhoods that lack playgrounds within walking distance, and community members are asked to raise some money for the project and participate in the construction. The playgrounds are built in a single day.

Imagine Southeast Public Charter School was chosen in part because the group wanted to celebrate its 2,000th project in Washington, where it is headquartered, said Karen Duncan, an adviser to KaBOOM! and the wife of Education Secretary Arne Duncan.

The group gets about 14,000 requests a year for new playgrounds, and Imagine Southeast stood out because its principal and parents were so enthusiastic about the project, Karen Duncan said.

The 4,000-square-foot playground cost $195,000 and was funded by the Knight Foundation, a charitable entity founded by the former owners of the Knight Ridder media company.

The Duncans also helped out with the construction, along with NBA veteran Antawn Jamison, a former Washington Wizard who’s now with the Cleveland Cavaliers. Jamison traveled to Washington from his offseason home in Charlotte, N.C., to volunteer his time. It was the fifth time he had worked with KaBOOM!

“You see the gratification when you see the smiles on the kids’ faces,” Jamison said. “I’ll be able to sleep good tonight, knowing that I made a difference.”

Jamison said he doesn’t often get starstruck but was thrilled to meet the first lady.

“I was surprised by how tall she was,” the 6-foot-9 power forward said.