Seven cities that are forging new bonds between traditional public schools and public charter schools received $25 million in private funds Wednesday to propel their progress.

The Bill and Melinda Gates Foundation announced multimillion-dollar grants to Boston, Denver, Hartford, New Orleans, New York, Philadelphia and Spring Branch, Tex., to deepen a new kind of collaboration between charters and district schools.

The seven cities are among 16 that have signed a compact, crafted in 2010 by the Gates Foundation, in which they pledged to break down the barriers between traditional schools and charter schools and work together to improve education in all schools. The District, where 41 percent of schoolchildren attend public charter schools, has not signed the compact.

All 16 participating cities have received $100,000 grants from the foundation. But the seven chosen cities will get considerably more money to further their efforts, ranging from $2.2 million for Spring Branch to $5 million for Hartford.

When public charter schools were conceived 20 years ago, they were envisioned as laboratories in which new teaching and learning techniques could be tested and then introduced into traditional schools. Charter schools were never intended to compete with traditional schools.

But as charter schools have grown — more than 5,600 public charter schools educate about 2 million students nationwide — relations with traditional schools have grown tense.

Charter schools are public schools run by private organizations, sometimes for profit. They often compete with traditional public schools for scarce tax dollars, students and other resources, such as school buildings.

Some traditional schools accuse charter schools of “creaming,” or enrolling the most-motivated students, leaving them with the ones who are harder and more expensive to educate. A Government Accountability Office report released this year said charter schools enroll fewer children with disabilities than traditional public schools. And most public charter schools are not unionized, posing challenges to teacher unions.

“There’s been considerable tension between traditional schools and charter schools, which is why we’re so thrilled to see the level of collaboration in these particular cities,” Vicki Phillips, of the Gates Foundation, said as she announced the grants in Philadelphia.

In that city, traditional public schools, charter schools and private Catholic schools have all signed the Gates compact. They are working together to create a training academy to produce up to 50 new principals each year, leaders who could work in charter, private or traditional schools, said Lori Shorr, chief education officer for Mayor Michael A. Nutter (D). The district and private schools also plan to work with Mastery Charter Schools, a high-performing cluster of schools, to learn best methods for teacher training, she said.

“It’s time to put adult foolishness aside, as the mayor likes to say, and start to talk about outcomes for kids and how we can learn from each other and not waste taxpayer money in duplicating services,” Shorr said.