Teacher David Henwood claims that GCSE pupils have had their design and technology exams incorrectly down- graded.

Mr Henwood, 48, has been a design and technology teacher at King Alfred's Community and Sports College in Wantage for five years. Before that he was a groundsman at the school.

The father-of-two, from Oxford, said he was also in dispute with colleagues over how raw materials from the course were disposed of.

This has resulted in him being placed on indefinite leave until the dispute over materials is resolved.

He said: "I don't think students in my GSCE classes have been treated fairly and I want the examining board to look at this, but I have been overruled."

Mr Henwood said that when he marked the pupils' written and practical coursework - about 60 per cent of the final mark - 95 per cent were a C grade or above.

But senior staff questioned his marking, and down- graded about 70 per cent of the pupils to E grades. They took the final exams in May.

Mr Henwood, of David Nicholls Close, Littlemore, questioned the downgrading and asked for the papers to be remarked externally.

He also appealed to OCR - the Oxford, Cambridge & RSA examinations board - asking it to intervene, but the board refused, saying it was an internal matter for the school.

Mr Henwood added: "One parent has already questioned his son's exam result, and I believe he's having the examination part of the paper remarked, but not the coursework.

"If his coursework was remarked, then the whole class's work would have to be remarked. The school didn't want that and allowed the September 20 deadline to pass.

"I believe pupils' exam marks have been downgraded incorrectly and I want OCR to intervene, or Ofsted inspectors if necessary."

Mr Henwood demonstrated outside the school's Portway site to highlight the issue.

He said he had no reason to believe that the exam section - worth 40 per cent of the marks - had been marked incorrectly, but due to the importance of the coursework, downgrading it had a big effect on the final grade.

School principal Nick Young declined to comment, but John Mitchell, of Oxford County Council's education department, said: "Coursework makes a significant contribution to GCSE results - consistency and therefore fairness of marking is a high priority.

"Mechanisms for moderating, or checking, that marking has been fair are well established in all schools.

"In this case, the coursework was moderated by two very experienced teachers. The school and county council have complete confidence in the revised outcomes.

"Mr Henwood's leave of absence is the result of an internal staff matter which is being dealt with, quite properly, by the school, with advice and support.