A Kent grammar school which operated its own admissions exam alongside the county's 11-plus selection test has been told the procedure is unfair.
The school had operated a dual-test admissions procedure
Kent County Council's (KCC) objections to the Folkestone Girls Grammar test were backed by the School Adjudicator.
The council said dual-test criteria confused parents, while the school said a previous adjudication had found "possible flaws" in the county's test.
On Thursday, the school declined to comment on the decision.
Cllr Leyland Ridings told BBC Radio Kent that other grammar schools in east Kent were also operating a dual-test system and it would be challenged next year.
He said the standard of the separate test used by a number of schools was "extremely high".
But he added: "I think we just felt it was entirely inappropriate in terms of clarity, fairness and objectivity for there to be two different sorts of tests."
The adjudicator's report said the "Dover test" was first offered by the Dover Grammar School for Boys, and later by Dover Grammar School for Girls and Folkestone Girls Grammar.
It said: "The test is used in the belief that it gives pupils from disadvantaged backgrounds the opportunity to perform better than they would on the county test if their vocabulary is impoverished.
"It is run in parallel with the Kent tests and only makes a material difference where a child is deemed to have passed the Dover test, but failed the Kent tests."
It said KCC had "no route for objecting the action" in the early 1990s, and allowed the same test to be applied at Dover Grammar School for Girls, because of "the apparently anomalous position created for families in the area".
But it said that Folkestone School for Girls had recently adopted the same test, after which the education authority took action to resolve the anomaly.
School adjudicator Dr Peter Matthews said the previous adjudication in 2005 had found possible flaws in the Kent-test but allowed the school's dual test for one more year to promote "further discussion".
He said the council had collated information and had not undertaken consultation, but he believed KCC had responded appropriately.