Few high schools, let alone those in cities, have hens, pigs, and sheep, a one-acre vegetable garden, or an extensive network of hiking trails. But Common Ground, in New Haven, Connecticut, is far from ordinary. The mission of this 200-student charter high school, which sits at the edge of a wooded, 1,800-acre state park, “is to instill environmental literacy in urban kids,” says Melissa Spear, executive director.

Since 1997, when the school was founded, Common Ground has expanded several times, always by adding onto its base of operations—a barnlike, wood clapboard structure referred to as the hilltop building because of its location on the steeply sloping campus. But about eight years ago, with its student body still growing, and with more summer, after-school, and community programs run by its parent nonprofit, Common Ground’s management team and board began to consider another expansion, issuing a request for proposals in 2011.