A half-billion-dollar study funded by the Bill and Melinda Gates will put the focus on the key element in improving education — good teachers. The Gates Foundation has spent about $2 billion over nine years on improving education in America's pubic schools. Now, the foundation is focusing on the most essential element, top-quality teachers.

Whenever employment contracts are being renegotiated, teachers unions argue that simply paying all teachers more — and all the same based on experience — will improve public education. But reasonable people realize that just paying the same teachers more money does not improve their performance or effectiveness.

Despite the teachers union's position, not all teachers are good or effective. Just as not all lawyers are the same caliber and not all accountants are superior and not all contractors are top quality. But identifying good teachers, as well as poor teachers, is an essential first step in improving public education.

Last week, it was announced that the Gates Foundation plans to spend $500 million over the next five years identifying what qualities are found in the best teachers and how to measure those qualities. This research will connect nicely with President Barack Obama's support for merit pay — for paying the best teachers more money. Obama also has expressed support, at the other end of the spectrum, for making it easier to remove the least-effective teachers from the classroom and replace them with better teachers.

Teachers unions have fought both these ideas for years, but few people outside the education bureaucracy would argue against getting poor teachers out of the classroom.

The credibility and clout of the Gates Foundation should help move merit pay and realistic mechanisms for enhanced teacher quality closer to reality.

The project is focused on developing the best methods for rating teachers. It also will work with a select group of school districts across the country, including Pittsburgh public schools, to find new ways to recruit, train and evaluate teachers.

Beyond that work, the Gates project supports using the best teachers as mentors, and finding ways to use money to motivate teachers and schools to improve. The group also supports making tenure more meaningful, and not a routine classification reached nearly automatically, and universally, with little or no evaluation of teaching effectiveness.

Developing proven methods for evaluating teachers makes sense, and should have some impact on compensation. Just as important, once the best teachers are identified and the qualities that make them more effective are understood, they can be used to help make other teachers better.

But even after being mentored and receiving additional training, some teachers still will fall short. And then, the system must allow for those people to leave the profession, in order to make room for higher-quality teachers.

Health care reform has been getting all the attention lately, but education reform is just as critical. And real change, not just tweaking around the edges, is required.

Evidence has been mounting for decades that American students are falling behind their counterparts in Asia and Europe. During his campaign for president, Obama promised to bring real change to education and improve America's schools. He knows that giving all teachers the same generous wage increases and benefits packages is not the answer.

The union's position that teachers are all the same and cannot be ranked or evaluated for effectiveness is nonsense and must be rejected. Students in any school know which teachers are best and which teachers are weak. Their parents generally know something about which teachers are good and which are not. And school administrators also know which teachers are good and which teachers are not good.

The Gates Foundation's work is important and could lead to exciting changes for schools and students. Teachers unions and an out-of-date tenure system must not be obstacles to improving America's schools.

Teachers have an important and difficult job. But it's time to overhaul the system so only the best possible teachers are in America's classrooms.