“Over the past four decades, the per-student cost of running our K-12 schools has more than doubled, while our student achievement has remained virtually flat,” writes Bill Gates in a Washington Post op-ed.  We can “flip the curve,” raising performance “without spending a lot more,” if we “measure, develop and reward excellent teaching.”

. . . of all the variables under a school’s control, the single most decisive factor in student achievement is excellent teaching.

. . . To flip the curve, we have to identify great teachers, find out what makes them so effective and transfer those skills to others so more students can enjoy top teachers and high achievement.

The Gates Foundation is working to develop “fair and reliable measures of teacher effectiveness” that will be endorsed by teachers and used to improve teaching, Gates writes.

These measures also could be used to determine teacher pay instead of the traditional system, which spends $65 billion a year to compensate teachers for seniority and advanced degrees. Redirect the money to improving achievement, Gates writes.

The 50-year campaign to reduce class sizes has been very expensive, but not very effective, Gates argues. “U.S. schools have almost twice as many teachers per student as they did in 1960, yet achievement is roughly the same.”

What should policymakers do? One approach is to get more students in front of top teachers by identifying the top 25 percent of teachers and asking them to take on four or five more students. Part of the savings could then be used to give the top teachers a raise. (In a 2008 survey funded by the Gates Foundation, 83 percent of teachers said they would be happy to teach more students for more pay.) The rest of the savings could go toward improving teacher support and evaluation systems, to help more teachers become great.

If we improve teaching, we’ll improve achievement, Gates concludes.

I think we also need to improve the environments in which teachers work. Yesterday, I ran ‘I don’t want to teach any more’ by a veteran teacher who feels overwhelmed by a large class with too many students with behavior problems, language problems and disabilities. High school teachers are trying to teach English, history and science to classes that include students who can’t read or can’t understand English; math teachers face a mix of algebra-ready students and kids who can’t multiply 4 x 5 without a calculator. We need strong principals who make it possible for competent teachers to teach well. I think we need to group students by learning needs rather than age.