Styrofoam cafeteria plates, the ubiquitous school-lunch staple, are a thing of the past in the Philadelphia School District.

As of last month, the system switched to compostable round plates made from recycled paper, joining a small but growing number of school systems that have pulled off the change across the country.

In the past, Philadelphia used 880,000 trays, plates, and bowls a month. All of them were destined for landfills after they were used, not breaking down for hundreds of years.

The shift will keep nine million pieces of Styrofoam annually out of landfills, officials said.

Businesses have moved away from polystyrene, which is made from nonrenewable petroleum, in recent years, but schools have been slower to do so.

Philadelphia's school system, moving toward a smaller carbon footprint, has long wanted to ditch Styrofoam, but it was trapped by cost: Polystyrene is cheaper than the Earth-friendlier alternatives, and school food service operates on the narrowest of margins, feeding the district's 130,000 students cannot cost the operating budget fund a penny.

Enter the Urban School Food Alliance, a coalition of the nation's largest district's food-service departments that has banded together to leverage their purchasing power and share tips on serving better food with better environmental practices. The group challenged the industry to come up with a compostable plate; a vendor in Maine came up with one at a price point districts can live with.

"It was a game-changer for us," said Amy Virus, Philadelphia's assistant food services director. "They were able to negotiate really good pricing that we could piggyback on and purchase from the vendor. We're really excited about finally making this change."

Philadelphia's move away from Styrofoam puts it in the vanguard. New York, Miami, Chicago, Los Angeles — also members of the Urban School Food Alliance — have made the change.

The new plate has five compartments, including a spot for a drink in the center. It's earned early raves from students, Virus said — it's sturdier, and the drink compartment means that students no longer need to use both a tray and a plate to juggle their lunches. And where a side dish like mashed potatoes or green beans often ended up in a bowl, now those too have been replaced by the single plate.

Compostable trays average $0.12 per piece, but the food-services group got the price down to about $0.05 each. That's still more expensive than the $0.04-per-item price for Styrofoam trays, but Virus said that because the district has largely eliminated the need for bowls and trays, it's able to absorb the price difference.

For now, most of the district's trays still are going into the landfill, but they eventually will break down, and officials hope a four-school composting pilot expands.

"We would love to have the schools and the students and staff on board to have more composting," Virus said. "This is a great potential opportunity."

Wayne Grasela, the district's executive vice president for food services, said representatives from the alliance's partner school systems now speak weekly, sharing insights and looking at items they purchase in common and how they can get more for their money.

"We're making sure we're getting the best value for the best cereal now, for instance," Virus said. "We're looking at lower-sugar cereals; that's the kind of collaborative work that can impact the food we're purchasing for our students."

Next on the food coalition's list? The group is exploring losing plastic utensils in favor of compostable ones.