“When you go into MS, you know you’ll get consistent quality,” the head of South Dartmoor Community College said. “It doesn’t matter if you’re buying fruit and veg or suits.”

The Devon secondary was among the 33 schools trialling Professor Reynolds’ project. Mr Tarleton hoped to reduce the 22 per cent gap between the number of A-C grades achieved in optional GCSE subjects in 2003 and those achieved in English, maths and science.

He introduced “learning hubs” during after-school training sessions. These were discussion groups, in which particular departments outlined the techniques they used. For example, the English department explained to science teachers how they carry out discussion work.

All staff were required to sit in on three lessons given by different departments, then produce bullet points stating what they had learnt.

Richard Woodland, a science teacher who observed an English lesson, said: “Because it doesn’t form part of the performance management schedule, it’s non-judgemental and non-critical. It’s about colleagues learning from each other and sharing good practice.”

By 2007, the difference between the number of A-C grades achieved in core and optional subjects had been reduced to 3 per cent.

Nonetheless, Mr Tarleton believes that tact is vital: “People are modest. If you set them up, they can end up being regarded as the head’s favourites. But there’s good practice everywhere now. Teachers should not be afraid to go and observe just about anybody.”