By Gary Eason Education editor, BBC News website

The biggest impact would be on schools with the best students

Education inspectorate Ofsted made errors in the annual performance assessment reports it produced on secondary schools in England.

Tables of subject-by-subject GCSE exam results in the reports - known as Pandas - omitted the top A* grades.

Ofsted has apologised to schools for what it attributed to a "programming error". It hopes to put out revised versions by this weekend.

The Pandas are the basis of inspectors' judgements about school effectiveness.

The omission in the initial 23 December versions meant performance in any subject in which students got the highest possible grade was underestimated.

The biggest impact would be on the schools and subjects with the highest achievers.

Inspectors

An Ofsted spokesperson told the BBC News website the problem affected the "subject indicator tables" in the reports - page after page showing every grade in every subject.

This re-release is part of the continual process of providing accurate, up-to-date performance information for schools Ofsted

Other analyses such as the headline percentage achieving at least five good grades had included the A*s, she said.

Another problem was that some GNVQ results for about 350 schools arrived too late to be included in the data.

"For these schools the measures in the Panda may underestimate performance.

"Inspectors have been made aware of this issue and schools that are being inspected are advised to discuss the issue with the lead inspector."

A third Panda report will be issued later in the spring term, based on the validated data used in the attainment tables produced by the Department for Education and Skills.

"Ofsted has written to all secondary schools to explain how the Panda report might be affected and how the issues have been addressed and to apologise for any inconvenience caused," the spokesperson said.

Asked how much the error had cost, she said: "This re-release is part of the continual process of providing accurate, up-to-date performance information for schools and is not viewed as an additional cost."