Two high-performing single-sex grammar schools look likely to become the first "hard" federation to divorce after staff at one of the schools said they wanted to withdraw from the project.
A consultation on whether to split the Boston Grammar Schools Federation has been launched after more than 50 per cent of staff at the girls' school, Boston High, said they wanted out.
The schools were brought together last year due to falling pupil numbers.
Boston High and Boston Grammar will remain federated, as they have been since 2007, while the consultation takes place but will operate as separate schools, and no longer share teachers.
The National College for Leadership of Schools and Children's Services said it "had not heard" of a federation seeking to split before.
The Department for Children, Schools and Families is encouraging schools to federate as a way to pool resources and support each other as rolls fall.
The concept has had a mixed reception in local authority areas where it has been carried out, because of fears schools could lose their identities.
Senior staff inevitably face uncertainty under federation, where an executive head usually takes charge of the overall project.
There is no record of the numbers of "hard" and "soft" federations, but preliminary research by the National College suggests there are 350 executive heads. Hard federations are when governing bodies are merged and the schools are considered one entity, whereas the soft version takes place when two separate schools agree to work together.
The reason behind the girls' school staff asking to withdraw appears to centre around plans to merge the schools into a single co-educational school on one of the two sites.
It is understood there is debate over which site should host the new building, with Boston Grammar supporters claiming that its long history, dating back to 1567, makes it more suitable. The grand, listed buildings, featuring stone crenellations, are famous in the Fenland town.
But others have argued the girls' school would provide more modern facilities for the merged institution.
It is understood that supporters of the boys' school also believe the executive head of the federation, Helen McEvoy, favours the girls' school site, because she was originally head there.
But its supporters have told The TES that she, and her leadership team, have been unfairly treated during the affair.
Ken Rustidge, Lincolnshire secretary for teaching union the NUT, said the federation of two such distinct schools would inevitably cause tensions.
He said: "People don't like change. These are two schools with very strong identities and traditions going back many years."
Refusing to comment directly on the case, Richard Bird, legal adviser at the Association of School and College Leaders, said: "Any break-up is likely to be traumatic and unhelpful in the short-term to all concerned. A local authority which promotes a federation has a duty to do everything that is within its powers to make it a success."
He added that the "storm of acrimony" surrounding feuding federations like this could put people off the job of executive head.
HIGH-FLYING SCHOOLS: THE RIVALS
Boston Grammar (pictured)
Latest Ofsted rating: Good
School type: Community school
Sex: Boys (girls admitted to sixth form)
Pupil numbers: 597
Percentage of pupils gaining five good GCSEs including English and maths: 83
Latest Ofsted rating: Good
School type: Foundation
Sex: Girls (boys admitted to sixth form)
Percentage of pupils gaining five good GCSEs including English and maths: 95