Researchers from Huddersfield University have found that pupils are much more likely to achieve five or more high-grade GCSEs in years in which their schools are not inspected. They discovered that, on average, 40 per cent of pupils achieved this benchmark in schools that had been inspected during their GCSE year. In schools that had not been inspected the average was 52 per cent.
Dr Sandra Daniels, the statistician who carried out the analysis, said: "It may be that the Office for Standards in Education chose to inspect a higher proportion of weaker schools during the four years covered by our study, but I have no evidence of this."
The researchers, who monitored 47,846 pupils in 426 secondary schools, also claim that inspections carried out between March and June have a particularly damaging effect on a school's GCSE results.
"The average results of schools inspected in September and October were nearly as high as those that weren't inspected at all, but only 28-29 per cent of pupils, onaverage, achieved five or more high-grade GCSEs in schools inspected in May and June," Dr Daniels said. "Some of the schools inspected during these months were weak anyway, but the inspection seems to compound the problem."
The Huddersfield findings have been challenged by OFSTED. "We have analysed the data on all schools - not just selected LEAs - and found no clear correlation between inspection and GCSE results," its spokesman said.
But this study is not the first to suggest that OFSTED's routine secondary inspections - which cost nearly pound;20,000 on average - are not helping to raise standards.
In January, Philip Hunter, president of the Society of Education Officers, produced a report on GCSE results in seven education authorities which suggested that inspection had not helped schools improve.
In May, Liberal Democrat education spokesman Don Foster and independent researcher Charles Bell announced that GCSE scores in inspected schools improved no faster than in non-inspected schools between 1993 and 1996.
Chris Woodhead, the chief inspector of schools, described the latter findings as "sensational and simplistic". But the Huddersfield team, led by Professor Cedric Cullingford, have produced even more controversial statistics after scrutinising GCSE results in Kirklees, Birmingham, North Yorkshire, Nottingham, Avon and the London borough of Kensington between 1994 and 1997.
Professor Cullingford said: "Whatever the inspection period OFSTED has a negative effect on the percentage of pupils gaining higher grades even though the proportion of pupils obtaining five or more higher grades has been increasing each year."
"The effects of OFSTED inspections on school performance", by Cedric Cullingford, Sandra Daniels and Jerry Brown, is available from Professor Cullingford, School of Education and Professional Development, Holly Bank Road, Lindley, Huddersfield HD3 3BP