Much of what Dylan Wiliam says makes perfect sense. The quality of the teacher is the ultimate arbiter of how well a pupil learns; and teachers improve their own practice most when collaborating with colleagues.

Some of his views are, however, more controversial - particularly in the current climate, focusing on class sizes. Professor Wiliam, to the disgust of bodies such as the Educational Institute of Scotland, argues that formative assessment is far more cost-effective than cutting class sizes. The latter is espoused by politicians “because teachers and parents like it”, according to the deputy director of the Institute of Education in London, who argues that whenever a class-size reduction programme is implemented, it leads to a dilution in teacher quality.

Many teachers would argue for both - the chance to improve their practice and to do so with smaller classes. They do not see the two as mutually exclusive. Professor Wiliam argues that it is not a question of teachers using formative assessment effectively or getting good exam results; good formative assessment encourages “mindfulness”, which means that, even if a student has not seen a particular question before, he or she is better at thinking about how to tackle it. Teaching to the test de-skills the child.

Too often, Professor Wiliam says, teachers attend an inspiring session of continuing professional development and return to school only to continue with their previous ways of thinking. His “WeightWatchers” model of teacher learning communities is intended to offer mutual support, but also to force teachers to be more accountable to their colleagues for carrying out what they promised to do at the last meeting. In theory, it should work. But there are practical obstacles - the time required of teachers to participate and their shifting population from one year to another. Let’s give him an A for aspiration.