Few education reforms or initiatives come with promises of quantifiable gains in achievement. But Paul Black and Dylan Wiliam of King's College, London, are specific about the improvement possible through the use of "formative" assessment or classroom evaluation in British schools.
Their conclusions are based on a year-long survey of 600 research studies across the world, involving 10,000 learners from nursery school to undergraduate levels. They conclude that teacher assessment which diagnoses pupils' difficulties and provides constructive feedback leads to significant learning gains.
The approach is a significant help to low attainers. The effect is to reduce the spread of attainment in a group while raising overall performance and so tackling Britain's apparently intractable problem of a "tail" of underachievement.
Researchers estimate learning gains by comparing experimental groups with classes taught and tested in the usual way. The experiments have produced consistent gains - from the United States to Saudi Arabia, and in subjects from maths to PE.
The survey indicates five factors crucial for success: regular classroom testing to adjust teaching and learning rather than to grade pupils; enhanced feedback between teacher and learners; the active involvement of all pupils; attention to motivation and self-esteem; and time for self-assessment.
Five factors that hinder learning are tests which encourage rote learning; failure by teachers to discuss and review testing methods; overemphasis on marks and grades; approaches which stress competition rather than self-improvement; and testing which serves a managerial rather than a learning function.
In the UK, the researchers argue, the role of formative assessment is hampered because almost all the resources and attention have been devoted to end-of-stage tests such as those under the 5-14 programme.