According to Oscar Wilde, “religion is like a blind man looking in a black room for a black cat that isn’t there, and finding it”. Well, in a way that is almost the definition of teacher quality.

Defining, let alone measuring and rewarding teacher quality is notoriously difficult. Anyone who claims the opposite is either naïve or blinded by ideology.

But just because it is hard should not be an excuse for not trying. At least compared to some overseas examples, we are not doing too well on evaluating teacher quality.

In New Zealand, we typically divide teacher performance into just two categories: satisfactory or unsatisfactory. Most teachers are classed into the ‘satisfactory’ group and receive automatic pay increases for the first eight years in the job. That’s basically it.

Now compare this with what is happening in Washington DC schools. In the US capital, they have overhauled their archaic appraisal system for the benefit of students.

The Washington model is based on clear expectations for teachers. It provides regular feedback and support; and it rewards the most effective teachers. So how do they achieve that?

Up to five times a year, a principal and a subject-matter expert observe and grade teachers on multiple aspects. They rate student progress, classroom practice, commitment to the school community, and core professionalism. They also capture the student voice through surveys.

Formal observations are unannounced but teachers can invite principals into their classroom for an informal and unscored evaluation.

At the end of each year, teachers are placed in one of five categories: highly effective, effective, developing, minimally effective, and ineffective. And teachers progress according to these rankings.

The Washington approach is both transparent and fair. Because of the regular feedback provided, teachers cannot be surprised by the final grade.

Designing the Washington system was hard. It took three years and hundreds of consultations with teachers, unions, and academics. But these efforts eventually paid off. Washington’s public school students have gone from some of the lowest performing in America to some of the fastest improving.

If teacher quality was a bit like trying to find a black cat in a black room, the Americans have shown us how to find it. They just switched on the light.