Grammar schools in England have been ordered to publish details about their admissions tests, which campaigners say will expose them to greater scrutiny and potential legal challenges.

The ruling by a first-tier tribunal required the Lincolnshire consortium of grammar schools to release anonymised results for children who sat its 11-plus entrance tests, including raw scores and results adjusted by their dates of birth.

Lincolnshire’s 18 grammar schools use age-adjusted “standardised” scores to admit pupils, but the group had refused requests to publish the full results until the court ruled that refusal was “not in accordance with the law”.

Campaigners said providing the data offered greater oversight into how 11-plus entry exams were administered throughout England, adding that the tests were not overseen by the government or Ofqual, the exam regulator for England, unlike Sats national assessments, taken by children of the same age, or GCSEs.

Nuala Burgess, the chair of Comprehensive Future group that campaigns against selective education, said: “The 11-plus test is used to decide the schooling of some 100,000 children a year and yet it remains unregulated. The Department for Education provides no guidance on its use and carries out no checks on its implementation. The 11-plus remains the only formal test used in any part of the UK which never comes under scrutiny, and how it is marked is shrouded in secrecy.”

Mark Fenton, the chief executive of the Grammar School Heads Association, said: “We are currently assessing whether or not this judgment has any implications beyond Lincolnshire but we do not believe that the information released will be of any practical benefit to parents.”

Although state-funded selective secondary schools were abolished in most of England from 1965 onwards, 163 still operate with an exemption from the school admissions code’s bar on admitting pupils by academic ability. Eleven local authorities are classed as highly selective, including Lincolnshire, Kent and Trafford, with about a quarter of pupils attending grammar schools.

The tribunal ruling follows a four-year battle by James Coombs, whose freedom of information request in 2020 for the consortium’s 2019 results was initially denied by the group and then by the Information Commissioner’s Office.

Coombs then appealed to the tribunal, which this week ordered the schools to release the data in an anonymised form. Grammar schools in Essex already publish similar data.

Coombs said he appealed because he believed there should be greater transparency around how 11-plus results are calculated, in particular how age adjustments are applied and to what degree pass rates vary from year to year. “It has long been common knowledge that the 11-plus results are age-weighted but this disclosure puts an actual figure on it. Parents can look at the data and see what difference it meant to their individual child,” Coombs said.

He said disclosure of the age-weighted scores could “pave the way” for parents to make legal challenges over their use. The data disclosed by Lincolnshire showed that even a few days difference in birthdays could alter the standardised score required to pass. In 2019, a child born in August needed 46 correct answers in the verbal reasoning test to pass, while a child born in September needed 53.

Critics of selective schools say 11 years old is too young to rank children by academic ability, while the reliance on test results favours families with access to tutors or private schooling.