A Roman Catholic middle school in Suffolk, described as outstanding in a recent Ofsted report, is to close and its staff made redundant.
St Louis Middle School in Bury St Edmunds will close four years earlier than expected under county council plans to abolish middle schools.
The Diocese of East Anglia told parents the early move, in 2013, was because their schools were interdependent.
Schools in other parts of Suffolk had already moved to the two-tier system.
In Bury St Edmunds, St Edmund's School would become a primary school for children aged four to 11 and St Benedict's a senior school for the 11 to 18 age group.
Suffolk County Council's plans to make the whole of the school structure in the Bury area two-tier are on hold because of funding shortages.
Closing in 2013
Catholic schools St Felix, in Haverhill, St Louis, in Newmarket and St Joseph's, in Sudbury, are already preparing to become primary schools dealing with pupils aged four to 11.
The final phase was to involve the three remaining schools in the Bury St Edmunds Area.
However, Suffolk County Council has had to delay the re-organisation of schools in the town.
"This delay has been particularly challenging for Catholic education as all of our schools are interdependent," a diocesan spokeswoman said.
"The Bury St Edmunds Catholic schools will move to a two-tier education system ahead of the local authority schools in Bury St Edmunds."
Steps are being taken for other Catholic schools in the area to take staff from St Louis Middle School which will close in 2013.