Another week, another set of headlines about “failing schools”. The latest story was in The Daily Telegraph: a Tory government would take more than 600 secondaries with the worst results out of local-authority control; parents had been “let down” by these councils.

This followed reports - in at least three national newspapers after the Budget earlier this month - on the extra attention ministers were devoting to these same “failing” institutions.

Moreover, the F-word is now an accepted way to describe schools whose performance is below the national average on a key government benchmark, if reporting in The Guardian and Financial Times is a guide.

How balanced is this coverage and the political pronouncements that preceded it? Any objective assessment must conclude that it is grossly unfair to the schools concerned, and has major ramifications for our education system. The almost casual way in which the word failure is being used in these stories also calls into question the motives of the politicians who are triggering the articles.

In the past year, the phrase “failing school” appears to have been redefined to mean one in which fewer than 30 per cent of pupils achieved the benchmark of five top-grade GCSEs including English and maths. The catalyst for this may have come last October, when Gordon Brown used his first speech on education as Prime Minister to highlight the 670 secondaries that fell below that level.

He was careful to stress that not all these schools were underperforming, but also pledged to “end failure”. He used the F-word three times.

Eleven national newspaper stories about failing schools followed. In the same month, Lord Adonis, the junior schools minister, talked about a “substantial tail” of underperforming secondaries, many of which had defective leadership, again linked to the 30 per cent figure.

Politicians are now using this statistic to outbid each other on tough action to be taken against schools deemed to be failing: Labour is threatening local-authority action plans and academies, while the Conservatives also talk about the schools becoming academies, or transferring to “charitable trusts and parent co-operatives”.

In one sense, their arguments would appear strong. As Michael Gove, the shadow children’s secretary, said this week, questions have to be asked about any school where fewer than a third of children reach a “decent” performance.

Yet absurdity and irrationality dog this debate. The national average last year on the measure of five GCSEs including English and maths was 47 per cent. So a school on 29 per cent is not actually operating that far below the national mean.

Then consider that the statistics that are the basis for the latest horror stories actually appear to show how modern schools have improved dramatically in recent years. In the mid-1980s, the national average performance expected of any child in O-level or CSE exams was equivalent to an O-level grade F. In 1990, only a third of pupils left school with five grade Cs in any subject. Taken at face value, these figures suggest a dramatic national improvement. They also beg the question: in the 1980s, were thousands of schools really “failing”, as the figures would imply? Does that word, with its sense of institutions literally falling apart, really describe most pupils’ experience of school?

Politicians now express horror that any child could leave secondary school without five GCSEs including English and maths. But it should not be forgotten that the GCSE exam was benchmarked against an O-level system that carried with it a guaranteed high level of failure. Grading standards have been, supposedly, held constant against the O-level.

That many children still fall short of what is said to be the crucial C-grade hurdle may say more about the fact that GCSEs are still largely a sorting and selecting device guaranteeing that some pupils are adjudged to be behind others in their achievement - for that, to a large extent, is their function.

But the most urgent fact to consider here is the weight of evidence showing how little of a school’s “raw score” exam results are explained by anything the school actually does.

As Professor Stephen Gorard of Birmingham University has argued, family background and a child’s educational starting point have been shown, statistically, to be more important in influencing GCSE performance than what schools do. Pupils from disadvantaged homes and those with poor primary results are not evenly distributed among secondaries, but concentrated in some of them.

The only logical conclusion follows: the fact that more than 600 schools are operating below the Government’s threshold may say more about the distribution of pupils than about any qualities of the schools.

This is not to deny that some schools are likely to be genuinely underperforming. But to spray the “failing” tag around indiscriminately is as unsustainable as it is dangerous.

In fact, a TES analysis of the phrase “failing schools“in national newspapers in the past 20 years shows the term was virtually unused before 1990, and has really come to the fore only since 1997, which happens to be the year when the incoming Labour government instituted a “name and shame” policy for struggling secondaries.

Alan Smithers, professor of education at Buckingham University, believes use of the term “failure” in this sense stems from a government need to justify its own alternatives to mainstream state comprehensives, such as academies.

The Conservatives’ plans suggest a similar motive. But the worry is that the politicians and much of the press are simply feeding a public anxiety about school management that is not borne out by the evidence. They also risk further demotivating thousands of professionals in some of the toughest jobs in education, not least through a sense of injustice about the indiscriminate way in which failure is being directly attributed to them.

Is this the ideal way to improve our schools? As teachers well know, undermining someone is not usually a good way to get the best out of them.

- Warwick Mansell’s ‘Education by Numbers: the Tyranny of Testing’ is published by Politico’s.

Warwick Mansell, TES curriculum and assessment specialist.