Tomorrow, education ministers and union leaders from the world's top performing education systems will meet to discuss approaches towards teacher appraisal. Most of us have been lucky enough to have had at least one great teacher in our lifetime. But what makes a teacher great? And who gets to decide? Students? Parents? Fellow teachers? Principals?

There are some countries where mentioning the phrase "teacher evaluation" around educators, teachers' union leaders and policy makers provokes a rise in the ambient temperature. Teachers in the United States and France have gone on strike over the issue and Britain's teachers' unions and those that represent head teachers found themselves on opposite sides of a recent debate about whether to base teachers' pay on their performance.

Nearly everyone agrees that school systems need to find a way to encourage promising teachers, reward those who have demonstrated their effectiveness, and remove underperforming teachers from the profession. And in the 23 countries that participated in OECD's Teaching and Learning International Survey (TALIS), 83 percent of teachers who had received appraisal and feedback considered them to be fair assessments of their work; of those, 78.6 percent found that the appraisals were helpful in developing their work as teachers. But agreement on how to measure teachers' skills is harder to come by.

Teacher-appraisal systems in most countries are still a work-in-progress -- where they exist at all. Some 13 percent of teachers in countries that participated in TALIS had never received any feedback or appraisal of their work from any source. This is partly because such systems may be costly -- in money and time -- to design and maintain. More often, though, it's because there is no consensus on what criteria should be used to measure teacher performance (student test scores? a teacher's ability to engage a classroom full of students? students' and/or parents' opinions? some or all of the above?); who should do the measuring (an inspector from a central education authority? the school principal? fellow teachers?); and how the results of an evaluation or appraisal should be used (to determine salary? to shape the trajectory of a career? to signal professional-development needs? to weed out ineffective practitioners?).

Stakeholders are already beginning to find common ground on a few issues. They note, for example, that while student test scores offer important information, they cannot provide a complete picture of teaching quality; multiple sources of evidence are needed for that. And they agree that teacher-appraisal systems must be part of a holistic approach to the teaching profession that includes high-quality teacher training and professional development, attractive working conditions, nurturing school leaders, and engaging teachers in innovation and reform.

The subject of teacher evaluation came up briefly during the first two International Summits on the Teaching Profession, both held in New York. This week, participants at the third Summit, which is being held in Amsterdam and hosted by the OECD, Education International and the Ministry of Education of the Netherlands, will be examining the issue in depth from their various perspectives as teachers, union leaders, education ministers and experts in education -- and perhaps, too, as former students who may have once had a great teacher. Consensus might be too ambitious a goal for this meeting; but a lively -- not to say provocative and passionate -- discussion is all but assured.

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