Metaphors and analogies are a tricky business. They open up a lot of possibilities but how they are acted out in practice is not always predictable. This particular metaphor challenges us in one sense, learning is like loosing weight, i.e. getting rid of a cultural stigma but in another sense opens up interesting possibilities: make the process of change a part of your life rather than something to which you have to go outside your normal routine. It would be interesting to follow this metaphor's life span to see if it gets anywhere.

Education expert scores points for slimmer training | Schools special reports | EducationGuardian.co.uk

"Weight Watchers understands that it's not about trying to change peoples' knowledge, but their habits. You have to help teachers break their habits," he told EducationGuardian.co.uk.

"The problem isn't that teachers lack knowledge and need herding into a hall and experts talking to them. Teachers know most of what you want them to know anyway and are aware of the research, but not how to put it into practice.

"If they make commitments to try something new in the classroom - based on research evidence - and are held to account by their colleagues on what they tried and how they did, they really learn from it," he said.