Eliza Klein, right, and classmates from the King Open School line up Tuesday to remind the School Committee of the push to switch to biodegradable lunch trays throughout the district. (Photo: Marc Levy)

Eliza Klein, Maya Ludtke, Risa Paley-Zimble, Lilly Sandberg, Kaya Mark and their peers at the King Open School are officially compost ambassadors.

The School Committee bestowed the title in a unanimous vote Tuesday. Member Fred Fantini suggested it in a literally last-minute motion at the end of a four-and-a-half-hour meeting addressing the budget for the upcoming school year and changes in how middle schoolers are taught. Committee members were packing even as they voted.

There had also been lengthy public comment that night, most by adults addressing budgetary issues.

When the five girls lined up at the lectern for their turn, it was a welcome break, and each spoke eloquently on an issue that probably surprised many in the City Hall audience: composting and other environmentally friendly steps that could be rolled out districtwide.

“You were the ones who helped us develop the composting program at King Open. But we would like to remind you that we created our composting program as a pilot program for all the Cambridge public schools,” Eliza said as introductory speaker. “We like being the first school to compost. We’re proud. But we don’t like being the only school to compost.”

The program resulted from a request by the King students in fall of 2007 — backed by a petition with hundreds of signatures — to replace the district’s Styrofoam lunch trays, which include a cancer-causing polystyrene, with biodegradable vegetation-based trays. But the expense made the switch impossible, the students were told. Biodegradable lunch trays generally cost more than $60 for a case of 500, while the same amount of Styrofoam trays go for about $25.

There were things students could do to build toward a switch, committee members said, including recycling and composting. The school’s composting program, run with the help of the city’s Public Works Department, began in March 2009 and by summer had kept 4,460 pounds of garbage from landfills. Lessons from the program have been added to the school’s curriculum, including as science lessons.

Now, the students said, others schools are interested in putting their own programs in place.

“We want to thank you for helping us make all these changes happen. We’ve taken the small steps you suggested,” Eliza said.

But it was time to take a big step, she said, and spread the program districtwide so it achieved the economies of scale needed to allow biodegradable trays.

Committee members weren’t able to act immediately on the students’ suggestions, but clearly relished their visit. The vote suggested the composting program would widen — again with students taking the lead for implementation.

If a laugh line Eliza delivered was any indication, that was fine. They were impatient to get started, considering their request was made in 2007. “That was a long time ago, so long in fact that now we have a new School Committee, a new mayor and a new superintendent,” she said.