While I have another story about teacher quality, I'm not trying to pick on teachers today. Good education is about more than just teacher quality, but both of the stories I'm including today make the point that research shows that teacher quality is a major factor that shouldn't be ignored. In this Washington Post op ed, Melinda Gates writes about the importance of teacher quality and her foundation's efforts to improve it.

One reason I am so optimistic about these developments is because, after decades of diffuse reform efforts, they all zero in on the most important ingredient of a great education: effective teachers. The key to helping students learn is making sure that every child has an effective teacher every single year.

Teachers are at the center of our strategy at the Gates Foundation. Since my husband and I started investing in education 10 years ago, our foundation has partnered with more than 1,000 high schools. Our grantmaking wasn't always oriented around effective teaching, but gradually we noticed that the schools with the biggest gains were those doing revolutionary work inside the classroom.

Bill and I see evidence of this every time we visit a school. The 82 schools across the country that have implemented the Knowledge Is Power Program invariably get excellent results from the very same low-income students who tend to struggle at traditional high schools. Last year, we traveled to KIPP Houston High, where 90 percent of the students graduate, compared with 65 percent for the city as a whole, even though KIPP's students are poorer than their peers in Houston's public school system.

The key to this school's success is its principal, Ken Estrella, and the 44 dedicated and talented teachers on his staff. In one class, we observed three teachers leading small groups of students in integrated bio-engineering and world health exercises. By urging students to ask penetrating questions about the diseases of the developing world, the teachers were simultaneously helping them master the basics of biology. The lesson plan bore no relation to the passive lecture format that prevails in many schools.

Empirical research confirms what Bill and I have seen in classrooms nationwide. Data show that an effective teacher has more impact on student performance than any other school-based factor. If African American students could be guaranteed teachers in the top 25 percent of their profession throughout high school, the gap between their test scores and those of white students would disappear.

So why hasn't education policy focused more on raising teacher effectiveness? The country has tried a lot of (outrageously expensive) reforms that don't improve student outcomes -- such as reducing class size by one or two students and paying teachers to get master's degrees. Part of the problem is that it's so hard to measure teaching. Anyone who has ever been inspired by a teacher knows that pedagogy is both a science and an art. Finding a sensitive instrument to evaluate it has been a huge obstacle. Tests yield clear numerical grades, but they can't measure all the intangibles that make a teacher effective.

To help surmount this logjam, a team of researchers (with support from the Gates Foundation) is working with more than 3,000 teachers in seven school districts to develop measures of teacher effectiveness. The project uses seven methods, including videotaping classes, analyzing test scores, and surveying teachers, students and parents.

The Measures of Effective Teaching project will yield a wealth of information that educators desperately need. It will help school districts nationwide make informed decisions about rewarding effective teachers. And it will help all teachers get better at their craft. If we can understand what makes a great teacher great -- precisely what they do that helps their students learn -- then we can encourage average teachers to adopt those proven methods.

I hope that this "Measures of Effective Teaching" project is successful. If they can come up with some criteria that both teachers and administrators can use to evaluate effective teaching, it will not only help teachers improve their own teaching, but provide a framework for teacher support and for a reasonable evaluation process.

I think that the poor quality of teacher evaluation systems really hampers educational improvement. Without a rational way to differentiate good quality teaching from poor quality teaching, how can you identify those who need extra help and how can you fairly hold people accountable? I'm grateful that the Gates Foundation is helping with this work. I hope they're able to come up with a final product that a majority of people can accept, support and utilize to improve the quality of teaching in public schools.