Many of the District’s traditional schools have fewer children than they were originally designed to hold, driving up the cost of maintenance. Meanwhile, the city’s fast-growing charter schools often struggle to find suitable real estate.

The solution, according to a study commissioned by the city government: Push traditional schools to share space with charters, city agencies and community-based organizations.

Such “co-locations” exist in a few places in the District. In Southeast Washington, for example, Malcolm X Elementary houses its own students as well as those from Achievement Prep Public Charter School. In Northwest, Sharpe Health is home to both a DCPS special-education school and Bridges Public Charter School.

But the District has been far less aggressive about sharing public school space than some other cities, notably New York, where the number of charter schools co-located with traditional schools grew quickly under former Mayor Mike Bloomberg.

Now the District is poised to begin pursuing co-location more aggressively, according to Deputy Mayor for Education Abigail Smith, whose office commissioned the D.C. government study. “It’s something that we support and that the chancellor is really interested in,” Smith said, referring to D.C. Schools Chancellor Kaya Henderson.

Co-locations aren’t always welcomed or easy: Put two schools with different cultures and missions into the same space, and there’s almost sure to be some tension. Co-locations need “substantial oversight and management” in order to work well, the study notes, and the District would have to build its oversight capacity from the ground up.

Co-locations do offer a way to use large public buildings more efficiently, but there are important questions about how much extra space D.C. traditional schools actually have.

According to the government’s study, D.C. school system only needs 7.4 million square feet, or about 70 percent of the 10.6 million square feet of school building space in its current portfolio.

But that calculation doesn’t account for the way space is actually used in the District’s historic school buildings, said Mary Filardo, a facilities expert at the 21st Century Schools Fund. The older buildings have larger hallways, stairways, lobbies and mechanical rooms than newer school buildings, for example, as well as large theaters, full-service kitchens and vocational education spaces.

Cutting the school system’s space to 7.4 million square feet would leave each of the system’s 45,000 students with less than 170 square feet, the average recommended for new buildings. That is “not a workable space allocation for our existing facilities and particularly not for projected growth,” Filardo said, pointing out that population projections suggest that the school system needs to be able to absorb thousands children in the coming decade.

“Co-location would have been an option more responsibly pursued before the 2008 and 2012 school closings; and if there were policies in place that enabled the city to manage charter growth and locations,” Filardo said.

It currently costs about $96 million to maintain and operate all of the school system’s space; the school system pays part of that bill, but the Department of General Services kicks in about $45 million.

The city is now seeking to minimize that infusion, in part because charter schools do not receive a comparable subsidy, and the law requires both sectors to be equitably funded. Co-located charter schools and organizations would chip in for school system maintenance, thus reducing the cost to the city.