THE NUMBER of Oxfordshire secondary schools ranked in the top 25 per cent nationally in a key performance category has fallen dramatically.

Government figures released today show that the total of county schools in the top quarter for their value added scores has gone down from 13 to two.

And the man responsible for education at Oxfordshire County Council admitted he was at a loss to explain the figures.

The CVA score measures the progress pupils have made from the end of primary school to 16 years of age.

It takes into consideration social and ethnic backgrounds, special needs, gender and age.

On the basis of the CVA measure - only two Oxfordshire schools, Cheney School, in Headington, and Cherwell School, in North Oxford, have been included in the top 25 per cent.

Last year, the county had 13 schools included in the top quarter - a drop that Michael Waine, the county council's cabinet member for schools improvement, said he found "concerning".

He added: "We are concerned and are working closely with secondary schools. I can't say why there has been such a drop.

"This measures an improvement within a particular year - and what it is showing is schools are not bringing about the same level of gain for students as they did in the previous year.

"We have written to all secondary schools early in the autumn term where appropriate. The school improvement officers, or SIPS, work with all secondary schools and are ensuring that they are being challenged to improve on their best.

"Headteachers and senior leadership teams across the county are taking up the challenge to do better.

"If they are not achieving in line with their CVA, they will be asked for clear views for how they are going to improve. The local authority itself is also working with supporting particular schools.

"What I can say is that it is something we are very concerned about and will be tackling."

Jill Judson, headteacher of Cherwell School, said: "I know, having been a headteacher at a grammar school, that they often, and quite rightly, achieve consistently high results.

"But CVA is fairer when you take into account the value that a school adds to pupils from year six, or key stage two, right through to the end of their compulsory education at key stage four. It measures improvement."

The county council was unable to provide a list of the schools that had dropped out of the top 25 per cent at the time of The Oxford Times going to press.

This week's results did, however, show improving GCSE results in Oxfordshire's schools.

The new figures show 48.1 per cent of the county's pupils achieved five or more A* to C grades, including maths and English, compared with 46.7 per cent nationally.

The previous year 47.5 per cent had achieved this, compared with 45.8 per cent nationally.

Topping the county's GCSE results for the second year running was the independent School of St Helen and St Katharine, in Abingdon, which once again achieved a 100 per cent pass rate.

Schools which made significant progress for GCSE results in 2007 included Bartholomew School, in Eynsham.

It increased its pass rate to 73 per cent from last year's 63 per cent and John Mason School, in Abingdon, which increased its pass rate from 44 per cent to 57 per cent.

At A-level, Oxford High School knocked Magdalen College School from the top spot.

But headmistress Felicity Lusk described the league tables as "irrelevant".