That’s one conclusion which might reasonably be drawn from today’s survey into the most - and least - polluted secondary schools in England.

The 10 least polluted schools are all independent. But that’s far from the whole story. Half of the 10 worst affected schools are London independents, whose fee-paying parents could presumably send their children elsewhere. It would be interesting to know if they do, now.

While foul air is unlikely to directly affct pupil performance, it is probably an added pressure, particularly on already-stressed communities. The National Asthma Campaign, which wants air pollution reduced to an absolute minimum, says one in five teenage schoolchildren is asthmatic. A third of child asthmatics lose a week of lessons through illness a year, 8 per cent a month’s worth.

Ironically, the school run is a major pollutant. Even more ironically, car passengers are exposed to far more airborne irritants than pedestrians. Perhaps it’s time to vote with our feet.