When inspectors from the Office for Standards in Education visited Priory School in Slough, Berkshire, earlier this year, they described it as “excellent”. Two-thirds of lessons in the 730-pupil nursery, first and middle school were good, very good or excellent, they said, and the curriculum leadership was outstanding.

The headteacher, Carole Evans, was delighted but the OFSTED report only confirmed what she and parents knew already: that grant-maintained Priory School is highly successful. It is also massively oversubscribed. This year, there were 187 applications for just 90 places.

Meanwhile, a number of her staff were recently chosen to feature in a National Numeracy Project video teaching key stage 2 maths. A quick glance at the first key stage 2 performance tables for Berkshire, however, reveals a very different picture: only 50 per cent of Priory School pupils achieved level 4 or above in the English test, compared with an average of 62.9 per cent for the authority. The maths figures were also disappointing: 56 per cent of Priory children scored level 4 or above compared with a local average of 58.2 per cent.

According to Mrs Evans, the discrepancy between OFSTED’s glowing findings and the school’s league table standing is due to the high proportion of pupils on the special needs register. Priory School, which serves two large council estates, has a designated unit for physically disabled children. Last summer, there were 57 statemented children on roll. Twelve per cent of these were in year 6 , when the tests are taken.

Some of these children, says Mrs Evans, were unable to sit the tests because of their disabilities - one pupil could only communicate through a switch - yet they were still included in the overall figures.

“When league tables were first talked about, we wrote to the DFEE (Department for Education and Employment) and said if the tables were there to inform parents then schools like ours should not have to include statemented children in the figures because it would give the wrong impression,” says Mrs Evans.

“They wrote back saying statemented children would not be separated for publication purposes, but parents would be able to interpret the results and would understand why our figures were lower than other schools.”

To an extent, she agrees. “Parents aren’t stupid. I’ve not received a single complaint about our performance. People are still keen for their children to come here.”

But she is unhappy about a system she believes is misrepresentative and fears the tables could have sinister, long-term effects. One possible outcome is that heads will become more selective about which children they take.

“Local authorities can make schools take children with statements of educational need, but unless there’s a willingness, and the school has a philosophy of encouraging these children to develop, they’re going to be unhappy and at odds with the system,” she explains.

She is also worried her staff will become demoralised. “My teachers work really hard but the tables downgrade what they do. At least this year we’ve had an excellent OFSTED report. Next year, we won’t have that boost and staff may begin to think, ‘What’s the point?’ “You’re not going to find a better staff of teachers than we’ve got here, but we’ll never achieve 100 per cent in the tests because of our statemented children.”