Donald Macintyre's Sketch: Calculating Cameron does his sums in the margins

Asked yesterday at Kingsmead School, in Enfield, by the man from 5 News what “nine eights” were, David Cameron decided to pass.

“I’m going to plead the Nicky Morgan defence,” he said. “I do times tables only in the car with my children on the way to school. I’m going to stick to that just in case I get one wrong on your excellent television programme.”

This did less than justice to his Education Secretary’s even more creative excuse earlier, when she declined to reveal on BBC Breakfast what 11 times 12 made: “I think that children at home are going to want to say, ‘I know better than the Education Secretary’.”

Of course! This showed sensitivity. No teacher wants to be told by an irritated pupil: “What are you asking me that for? Of course it’s 132. Even the Secretary of State for Education knows that.”

Nevertheless this hardly set a good example of what Ms Morgan, warming up at Kingsmead for the PM, said “I like to call the ‘culture of can’”. Was she about to lecture us on Andy Warhol’s Campbell’s Soup tin masterwork?

No, this was merely her buzz-phrase for the PM’s election education launch, his speech heavy with slightly scary slogans like “We will provide a good primary school place for every child – with zero tolerance for failure”.

As if this sinister hint that underperforming 11-year-olds – or at least their teachers – might be sent to boot camps or worse was not enough, he added: “We are waging war on mediocrity.” Which sounded oddly like “weaponising” education. Up to a point, because when he said that education spending would be going up, he meant it would be going down (in real terms). Or as he put it (possibly – and justifiably – thinking that no one would know what he was talking about), “in Treasury-speak flat cash per pupil”.

Schools that were failing – or even “coasting” – would be turned into sponsored academies. Asked about academies which were also failing, he gave a long answer which seemed to amount to: “We’ll turn them into academies again.”

But he was lyrical about schools like St Luke’s Portsmouth where, in 1999, “not a single pupil got five good GCSEs”. But now it was a Charter Academy, 79 per cent did. (He omitted to say it had become an academy in 2009, when Labour was in office.)

At the end, Kingsmead’s deputy head boy sensibly asked him why Cameron had come there. Because, the PM explained, Kingsmead, a flourishing academy, was a great school. He didn’t say: “Because Enfield North is a highly marginal constituency, my young friend.” Which, like “72” earlier, would have been the correct answer.