Mill Hill county school in north London was among two schools to have their selection cut back in the latest batch of rulings by the Office of the Schools Adjudicator.
But headteacher Dr Alan Davison says the decision is politically motivated and ignores the views held by most parents. Possible High Court legal action - a judicial review of the decision - was considered at a meeting of governors and teachers as The TES went to press.
An adjudicator last week ruled that the school had to reduce its existing partial selection, based on ability and aptitude (in technology, music or dance) from 45 per cent to 10 per cent on aptitude alone.
The decision was based on objections from the minimum 10 parents and Barnet Council.
The objectors said that partial selection worked against the interests of local children by limiting their choice of schools.
John Clark, the adjudicator, said: "The reputation of the school in technology, music and dance will encourage interested pupils and parents to make the school their first preference without the need to limit...the opportunities of local pupils to attend the school."
But Dr Davison has responded that the objections were not an accurate reflection of pro-selection feelings among parents at the 1,400-pupil school.
"They scraped together nearly 20 objections and sent more than 300 letters of support," he said. "We believe that the decision that was made was a political one," adding that it removed an important element of choice for local parents.
In another decision by admissions adjudicators, partial selection at the Sir Christopher Hatton School in Wellingborough, Northamptonshire, was cut from 15 per cent to 10 per cent.
Two schools in the area - Weavers and Wrenn - and Northamptonshire education authority complained that some children in feeder schools had failed to get places since partial selection was introduced.
They also said Weavers school's profile had suffered because higher-ability pupils had been "creamed off" to the other school.
But an adjudicator ruled that Erith school, in South London, could retain its 60-pupil-a-year partial selection procedure.
Chief adjudicator Sir Peter Newsam said the findings "illustrate the wide variety of local circumstances which adjudicators must and do take into account".