Microsoft co-founder Bill Gates announced Thursday that his foundation will invest more than $1.7 billion in public education, money that will go to support schools interested in developing and testing new approaches to teaching.

"Every student should get a great public education and graduate with skills to succeed in the marketplace," said Gates, who delivered the keynote address before about 1,000 school officials at the Council of the Great City Schools conference in Cleveland. "The role of philanthropy here is not to be the primary funder, but rather to fund pilots, to fund new ideas, to let people — it's always the educators coming up with the ideas — to let them try them out and see what really works super well and get those to scale."

The Bill & Melinda Gates Foundation has spent at least $3.4 billion on public education in the United States, most notably to develop the Common Core State Standards and to persuade state education leaders to implement them. His money also went to support charter schools, teacher preparation programs and an array of other improvement initiatives, including one to break up large high schools into smaller ones.

[How Bill Gates pulled off the swift Common Core revolution]

His investments have had mixed results, some of which he outlined in his address Thursday. The initiative to break up large high schools was not one that could be easily replicated elsewhere, he acknowledged. He also said he would no longer directly invest in developing models to evaluate teachers. His other models — which pushed districts to use test scores to size up teacher performance — were often controversial among educators.

Gates outlined his new investment in broad terms, saying that 60 percent would go to traditional public schools — an announcement that elicited applause in the audience of big city school superintendents — and that he wants to let schools and educators drive the process.

"The actual tactics about great teaching, about how to reform the schedule, how to get students who are off track on track — those will be driven by the schools themselves," Gates said. "We will let people come to us with the set of approaches they think will work for them in their local context."

The foundation will serve as a catalyst for change, Gates said, investing in new methods of instruction and then rigorously tracking student outcomes so that other districts can learn from the classrooms that serve as testing grounds.

Rick Hess, the director of education policy at the conservative-leaning American Enterprise Institute, said Gates's propositions have been all over the map and the foundation's latest pitch seems to represent another change in direction. Hess noted that a dozen years ago, the billionaire declared U.S. high schools to be "obsolete." Now, Gates is relying on educators to come up with the ideas to improve student achievement.

"It feels like they have pivoted through a number of strategies over the last decade or two," Hess said.

Another 15 percent of the money will go to help charter schools better support the needs of students with disabilities. The remainder of the money "will be focused on big bets," Gates said — research and development in education.

The Gates Foundation plans to issue a "request for information" on Monday, asking schools and other education organizations to submit ideas for how they might spend the money. It will issue an official request for proposals next early next year.

Hess said it was difficult to determine how the money would make a difference in schools. But he lauded Gates's intentions to improve education.

"We do have to experiment. We do have to learn things," Hess said. "We want to have people put their time and energy and resources into making schools better."

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