In an effort to encourage collaboration between charter schools and traditional neighborhood schools, the Bill and Melinda Gates Foundation has awarded $25 million in grants to seven cities.

The Gates Foundation, which is one of the largest philanthropic players in public education, was scheduled to announce the grants on Wednesday to Boston, Denver, Hartford, New Orleans, New York, Philadelphia and Spring Branch, Tex.

Relationships between traditional public schools and charters, which are publicly financed but privately operated, are often fraught, with neighborhood schools seeing charters as rivals for money and the most motivated students.

Charter schools, which have been operating in the United States for two decades and now educate about two million children across the country, were originally conceived as places to experiment with new ideas in education that could be transferred to their traditional counterparts. But that transfer has not often taken place smoothly.