Encouraging pupils to provide good feedback to their teachers on what they do and do not understand is the single most effective way of improving education. Reducing class sizes, the SNP Government's key project, is said to be among the least effective.
The findings are from what is believed to be the largest ever overview of education research, involving a synthesis of more than 50,000 individual studies covering all aspects of schooling in most of the English-speaking world.
The research, published in a book this week, is by John Hattie of Auckland University, who has spent the past 15 years analysing the studies, which cover at least 83 million pupils. The work is informing a new system, Visible Learning, which he has developed and is designed to improve teacher-pupil interactions.
Professor Hattie has created a league table of the most effective interventions designed to raise achievement, out of 138 possible approaches to raising standards.
Top-rated is pupils assessing themselves: reaching a view on their levels of understanding, and feeding this back to their teachers. This suggests there is a high correlation between the levels of progress pupils believe they have made and their actual performance in tests. He said this undermined the case that pupils needed constant external assessment.
Others featuring in the top 10 include formative assessment (using assessment to decide pupils' next steps in learning), "teacher clarity" (teachers being explicit in what they want their charges to do), "reciprocal teaching" (pupils taking turns to teach the class), and "feedback" from pupils to teachers and vice versa.
Reducing class sizes, he found, was towards the bottom of the rankings in terms of effectiveness, at 106th. Professor Hattie says that, while in theory cutting class sizes could be beneficial, this would only be the case if teachers changed their teaching strategies in smaller classes. This tended not to happen.
He told The TESS that teachers needed to use information they gained on pupils' understanding to set them more challenging work. "Teachers' job is not to make the work easy. It is to make it difficult. If you are not challenged, you do not make mistakes. If you do not make mistakes, feedback is useless."