Ever since Americans sent their children to one-room schoolhouses, parents have known what makes a good school: inspiring, organized, and creative teachers. But researchers haven’t been able to quantify what, exactly, makes a teacher effective and how to tie that to student achievement.

Now, the Bill & Melinda Gates Foundation–one of the most influential voices in education policy today–hopes to end that confusion. Nine years and $2 billion into its work to improve America’s public schools, the Seattle-based foundation is turning its focus to teacher effectiveness.

“We’ve been sort of looking around for the silver bullet for education reform, and actually the answer has been right under our feet the whole time,” said John Deasy, deputy director of the foundation’s education work.

Over the next five years, the foundation plans to spend another half a billion dollars in its quest to figure out what qualities make the best teachers and how to measure those qualities in the classroom.

The project has two parts: research to develop and test methods to rate teachers, and experiments at a handful of school districts around the nation to try out new ways of recruiting, training, assigning, and assessing teachers.

Among those asked to submit proposals for a share of the money were school districts in Atlanta; Denver; Hillsborough County, Fla.; Memphis, Tenn.; Omaha, Neb.; Palm Beach County, Fla.; Pittsburgh; Prince George’s County, Md.; Tulsa, Okla., and a group of Los Angeles charter schools.

This week, the foundation chose five finalists: Hillsborough County, Memphis, Omaha, Pittsburgh, and the Los Angeles charters. Final decisions will be made this fall.