After seven years and millions of dollars, Bill Gates says his foundation is perhaps not even a quarter of the way towards its goal of improving teacher quality, but he’s doubling down on the effort.

In his first major education speech in eight years, Gates said that he believes that he is “working on the right problem.” That problem, he said, is teachers who are unprepared, unsupported and ineffective – especially in low-income schools.

His speech got a warm welcome Wednesday from a hand-picked audience in Bellevue, Wash., outside Seattle. But several education experts expressed doubt that focusing solely on teacher quality could result in 80 percent of high school students graduating prepared for college – the goal the Bill & Melinda Gates Foundation has set for itself. (The Bill & Melinda Gates Foundation is among several funders of The Hechinger Report.)

Gates said that evidence showed that a good teacher could dramatically improve learning, and argued that top-quality teachers “would completely close the income inequity of learning in the entire country” if they were in place for three years nationwide.

Since 1999, the Gates Foundation has spent $980 million on improving teacher effectiveness, according to a foundation spokeswoman.

Related: Five ideas to improve teacher quality

Gates praised his foundation’s first U.S. education initiative, which spent $2 billion to help create small high schools. Gates said that he still believes that small schools improve learning, but that the shift in emphasis to teacher quality in 2008 had produced more systemic results, even though the change of course left educators disappointed and some fledgling schools suddenly without funding.

“We saw only some of those schools had substantial increases in college readiness, and we saw that spreading this idea of smaller high schools, we weren’t going to be able to get that adopted nationwide,” said Gates, “so having that as our primary tactic we decided wouldn’t achieve our goals.”

Although some education reform advocates appreciated the kind words for charter schools that were sprinkled through both Bill and Melinda Gates’s remarks, they said there wasn’t solid evidence to back Gates claims that teacher improvement would help significantly improve education for low-income students.

“If you believe that the system is fundamentally broken, you have to fix the system to get better results,” said Michael Petrilli, president of the pro-reform Thomas Fordham Institute, which also receives Gates funding. “I suspect that a foundation like Walton that is focusing on charters will see better results.”

In a subtle shift in the teacher evaluation debate, Gates seemed careful not to use language that has provoked teacher backlash against the reform movement. He never spoke of a need to fire “bad” teachers, and he said that test scores, while a “key outcome,” were only one way to measure teacher quality.

“The area we need to invest the most in is the idea of classroom observation,” followed by constructive feedback, said Gates. “I never met a teacher who said, ‘Yeah I got those test scores and now I know what I need to change.’ ”

Gates began his speech paying homage to Lyon Terry, a Seattle fourth-grade teacher who was Washington state’s 2015 teacher of the year. But Gates never mentioned teachers unions, nor did he mention the fact that Terry was a strike captain during last month’s strike by his union, the Seattle Education Association, which was one of the biggest strikes in the past decade.

In addition to lowering class size and extending the school day, that strike got rid of a teacher evaluation system that had been using student test scores to rate teachers.

Related: Once sold as the solution, small schools are now on the back burner

“I agree with Gates about the general concept that teachers are asking for support to work on their practice and get better – they’re crying out for it,” said Jonathan Knapp, president of the Seattle Education Association. “But the devil’s in the details.”

Gates singled out three places as evidence that the focus on teacher quality was bringing in big results – Denver, Washington, D.C., and Kentucky.

“I am confident that we have the solution: effective teaching, and our growing knowledge about what it is and how to spread it,” Gates said.

Knapp, like others, disputed whether the results in Denver were ones worth emulating (the district relies on merit pay), and whether they were tied to the reforms Gates was touting.

“There have not been improvements related to Denver’s teachers improvement program,” said William Penuel, professor of learning sciences and human development at the School of Education, University of Colorado Boulder. “Denver has had lots of turnover, and the working conditions for teachers have actually worsened.”

The National Education Association, the nation’s largest teachers union, released a statement cautioning that student needs “both inside and outside the school building” must be addressed, if education is to be substantially and systemically improved.

This story was produced by The Hechinger Report, a nonprofit, independent news organization focused on inequality and innovation in education. Read more about teacher training.

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Meredith Kolodner

Meredith Kolodner is a staff writer. She previously covered schools for the New York Daily News and was an editor at and for The Investigative Fund at the Nation Institute. She’s also covered housing, schools, and local government for the Press of Atlantic City and The Chief-Leader newspaper and her work has appeared in the New York Times and the American Prospect. Kolodner is a graduate of Brown University and Columbia University’s Graduate School of Journalism and an active New York City public school parent.