Observing lessons by colleagues who teach the same subject has become common practice. But research has found that teachers are better off sitting in on classes in other departments. It also suggests they can gain more from observing such high-achieving departments than from visiting other schools.

David Reynolds, professor of education at Plymouth University, piloted a scheme in 33 primaries and secondaries in which less successful departments learnt from more successful ones. He found that in most schools the difference between departments reduces significantly after three years. Most also increase their value-added scores.

“While not every school is effective, all will have within themselves some practice that is relatively more effective than elsewhere in the school,” he said. “Every school can therefore look for generally applicable good practice from within its own internal conditions.”

He points out that, over the three years, half of all schools have at least one subject with results in the top 20 per cent nationally.

Those schools with the greatest variation between departments tend to be the least effective, and such variation is rarely reduced by professional development courses.

The stress of teaching exacerbates these differences: good teachers thrive on chaos, while poor ones struggle. And government initiatives only increase this gap further.

Professor Reynolds insists that this is unacceptable: “Schools that are consistent performers are intolerant of large negatives, reduce variation in teacher performance and are reliable and consistent.”

His pilot project achieved more than improved results. It also helped schools identify key teaching methods that could be applied across the entire school. Departments also became more effective at communicating with each other.

And department heads began to feel more trusted. “In most schools, these roles had been historically ... regarded as an infliction on the people holding them, rather than ... offering an opportunity for personal and professional development.”

But schools should not expect immediate change, Professor Reynolds said. A very British sense of modesty can prevent effective departments from volunteering to help. And teachers can be resistant to the idea of comparing practice across departments.

“Change may be bitty, messy and chaotic at first, and progress will come in bursts and fits and starts,” he said. “But the vision ... needs to be held on to.”

‘Schools Learning from their Best’ is available at: www.ncsl.org.uk.