Claims that up to one million children are receiving a sub-standard education in 1,500 schools grabbed the headlines this week.

Less attention was given to figures published on the same day by Ofsted, the inspectorate, which painted a radically more positive picture. They showed that the numbers of schools that are officially “failing” has fallen to its lowest point since the first full year of inspections a decade ago.

The mutually contradictory reports raise questions about how failing schools should be defined and whether fears of declining standards have been exaggerated.

The pessimistic findings were published by MPs on the Public Accounts Committee. They concluded that 23 per cent of secondaries and 4 per cent of primaries were not reaching the standards laid down by Ofsted and the Department for Education and Skills, either because they failed inspections or had poor exam results.

Committee chairman and Conservative MP Edward Leigh said that almost pound;840 million spent on improving school performance had not tackled failure sufficiently.

“To waste so much human potential in this way is a tragedy,” he said. “The consequences in the long term for the pupils themselves and, more widely, for our society will be severe.”

In contrast, the Ofsted figures showed that at the end of the summer term this year 208 schools were in special measures, down from 242 last year and less than half the peak number of 519 nearly a decade ago. Some 312 schools fell into Ofsted’s “requiring significant improvement” category, and 117 had serious weaknesses, a label which is being phased out.

Added together, the number of schools on Ofsted’s lists of concern total 637, less than half the number published by the MPs’ committee. Estimates based on average school sizes in England would suggest they teach a maximum of 268,000 pupils rather than one million.

The reason for the difference is that, as well as schools in special measures, the PAC report also classified all schools where less than 20 per cent of pupils achieved five GCSE A* to C grades as being sub-standard.

This approach was heavily criticised by teaching unions. Steve Sinnott, general secretary of the NUT, called the findings a “gross simplification”.

He said: “There may be any number of reasons why any particular school is experiencing difficulties but that certainly does not mean those schools are failing their children.

“This is an alarmist scare story. Parents should be reassured that their children are receiving high quality education in the vast majority of the country’s schools.”

The Prime Minister also criticised the committee for including the schools with low exam results. Tony Blair said: “They are changing the definition of what is a failing school in order to include a whole series of schools that aren’t failing in the traditional definition but simply aren’t performing as well as they should be.”

The Ofsted statistics show that 137 primary, 54 secondary, six special schools and 11 pupil referral units are now in special measures.

The secondary school total is barely 10 per cent of the 500 secondary schools recently identified by Sir Cyril Taylor, the head of the head of the Specialist Schools and Academies Trust, as seriously underperforming at GCSE.

An Ofsted spokeswoman admitted that closures, such as the 16 failing schools which shut between April and August this year, had contributed to the apparent improvement in results.

But she said: “As a proportion of inspections carried out, the number of schools in special measures has fallen significantly.”

Professor Peter Tymms, from Durham university’s school of education, said judging schools by raw exam results and league table positions was ridiculous.

“Raw results reflect a school’s intake. Having a go at schools at the bottom end of the tables is very unfair. By that logic, special schools are failing schools.

“It is not right to say teaching must be bad in schools at the bottom end of tables. That’s not true: it’s dangerous and it harms the school to say that.”

* eader 20 Improving School Performance by the PAC is at www.publications.parliament.uk’Data on Schools Causing Concern - Summer Term 2006‘is at www.ofsted.gov.uk

FAILURE FACTS

1,557 Schools underperforming according to the Public Affairs Committe (PAC)

208 Schools placed in special measures and classed as failing by Ofsted

637 Total primary, secondary and special schools on all of Ofsted’s lists of concern, including special measures and serious weaknesses

500 The number of secondary schools seriously underperforming, according to Sir Cyril Taylor, head of the Specialist Schools and Academies Trust

54 The number of secondary schools in special measures

980,000 Pupils receiving a sub-standard education according to PAC

268,000 Estimated maximum number of pupils who go to schools on Ofsted’s lists of concern