This was what saved teachers in the 1970s: the pressure for more central control was already building, but what with the miners, the International Monetary Fund, the IRA and the hike in oil prices, ministers had too much on their plates to bother. Do not complain about absent prime ministers, putting the world to rights. A prime minister visiting Syria, Australia or Sierra Leone is harmlessly occupied; a prime minister visiting a Lincolnshire school or a Birmingham hospital means trouble.

Last week, The TES reported that Stephen Timms, the schools standards minister, had been visiting the Adam Smith Institute, the free-market think tank. That means trouble, too. According to its website, the institute is “constructing a new reality”. Its big idea is vouchers.

Conservatives have mostly seen vouchers as a way of boosting the private sector. They think it unfair that private school parents should pay for education twice over, once through their taxes, once through fees. If every parent were to be issued annually with a voucher, which could be redeemed either for a free year’s schooling in the state sector or, topped up with hard cash, for a place in a private school, this injustice would be cured, and there would be joy in the stockbroker belt.

But vouchers were originally a left-wing idea, which came out of California in the 1960s. The left wanted a way of getting better schools for disadvantaged children, and of empowering their parents. The proposal was to give parents “weighted” vouchers, so that a child from a poor home would be worth, say, twice as much as one from a rich home. Poor parents would then have greater influence over schools, which would have an enormous incentive to recruit disadvantaged children, particularly if they had the freedom to set their own teachers’ salaries.

Needless to say, I prefer the left-wing to the right-wing idea. I am not against markets if they can be rigged to the advantage of the poor. Alas, I cannot see the middle-classes tolerating it. They would demand the right-wing principle as well: the freedom to use the voucher, plus cash, for an exclusive private school.

This is the trouble with the schemes that Timms will have heard about at the Adam Smith Institute. They look well on paper; in practice, they will lead to all sorts of unintended side-effects. The same applies to proposals for paying private firms by results: for example, raising a child’s reading age by one year within a specified time. They would lead to a contract culture, which encourages people to cheat, to find ways of blaming others when anything goes wrong, and to concentrate on narrow targets to the exclusion of wider objectives. We would end up with a Railtrack of the classroom.

The railways indeed provide a salutary lesson. I have no doubt that the people who drew up the privatisation plans were terribly proud of them. But the reality of the railways was that, after years of underfunding, they were falling apart. A new reality could not be constructed out of privatising them.

Likewise in the classroom, the reality is that poverty is the biggest single drag on children’s learning: those who suffer from poor diet, bad housing, overcrowding and family instability do less well at school than those who live in better circumstances. Every teacher in the world knows that. If Britain has a standards problem, it is because one-third of the nation’s children were living in poverty when the Tories left office in 1997 and new Labour can reduce this proportion only slowly.

So the best way of raising school standards is to reduce poverty. That, not a voucher scheme, would construct a new reality in the classroom.

Peter Wilby is editor of the New Statesman.