David Bell called on teachers to “go the extra mile” to make a difference to children who live in poverty and whose families are “up against it on a daily basis”.

In a wide-ranging speech to pupils at Hermitage school, Chester-le-Street, County Durham, he said: “It grieves me each year ... to report on the extent of the gap between the best schools in the country and the least effective. The gap is still too great and if it is narrowing it is taking too long to narrow.”

Mr Bell praised improvements in schools during the past decade but attacked teaching standards of the 1960s and 1970s, describing them as “crackers”.

“I saw too many incoherent or non-existent curriculums, too many eccentric and unevaluated teaching methods and too much of the totally soft-centred belief that children would learn if you left them to it,” he said.

The challenge for schools now is to deliver a curriculum that balances basic English and maths skills with wider opportunities in subjects such as sport and music, he said.

Mr Bell also warned against allowing globalisation to turn education into a commodity, which like fast food, is becoming increasingly similar in different countries.