A secondary school has been banned from picking 10% of its pupils based on their "aptitude" for technology.
Critics of selection say 'aptitude' is the same as 'ability'
George Spencer School, in Stapleford, Nottinghamshire, was found not to be running a fair system of selection.
Under government guidelines, specialist schools can pick some pupils on natural "aptitude" but not on "ability", which assumes prior knowledge of a subject.
The Office of the Schools Adjudicator found that George Spencer was actually selecting by ability.
Nottinghamshire County Council made the complaint, arguing that the system in place undermined fairness.
The dispute reflects a larger one within education over the role of selection in specialist state schools.
Opponents say choosing some pupils by aptitude is a "back door" way of ranking them according to academic performance.
The government denies this, arguing that natural aptitude, and ability measured by looking at a child's academic achievement, are distinct.
George Spencer School, which specialises in technology, picked one in 10 pupils based on aptitude in the subject.
This was decided by head teachers at local primary schools, who graded children on a five-point scale.
The schools adjudicator ruled that the term "aptitude" should mean the same as a "gift or talent", which did not rely on previous experience in the subject.
But, as pupils' aptitude for technology was decided by head teachers, this was more like a measurement of "ability" - the same as "attainment" or "achievement".
George Spencer's system was "clearly" based on "ratings of attainment, based on a taught curriculum in design or IT".
The adjudicator also found that the primary heads making the decisions had "different standards", and that the "simple 'tick-box' exercise" lacked detailed instructions for those completing it.
This meant primaries which had a good relationship with George Spencer and more experience of the system could have an advantage.
But the school said that pupils who got in through their aptitude for technology had a wide variety of scores in other subjects.
This meant it did not choose any of its intake by academic ability, it added.
In 2004, the government said it would not allow specialist technology schools to introduce selection by aptitude.
But those, like George Spencer, which already had the system in place would be allowed to continue.
Previously, the Commons education select committee had found no difference between aptitude and ability, and demanded that selection by aptitude should be scrapped.
Most of England's secondary schools are specialists.
Those which focus on arts, sports, music or modern languages can select up to 10% of pupils by aptitude.
Schools which specialise in maths, science, engineering, business and humanities cannot.