The multi-academy trust that runs three primary schools in Blackbird and Greater Leys will join a larger schools group.
Blackbird Academy Trust (BAT) schools, which oversees more than 1,000 pupils at Orchard Meadow School, Pegasus School and Windale Community School, will transition to United Learning by the end of the academic year.
Trustees and the three headteachers of the trio of schools agreed that working with a bigger trust would improve the quality of the schools in the long term.
Chris Jones, chairman of BAT, said: “It is our responsibility to secure high performance over the long term and we concluded some time ago that this could best be achieved under a bigger parent trust with deeper resources.
“After very thorough review we are delighted to have reached agreement with United Learning to merge BAT schools with them.
“United Learning has the track record, the resources and the values which we believe will greatly benefit the pupils, staff and parents of Orchard Meadow, Windale and Pegasus.”
United Learning already runs schools in Banbury, including North Oxfordshire Academy and Hanwell Fields Community School, as well as other academies and independent schools across the country.
Its chief executive, Jon Coles, said the partnership would speed up improvements at the Oxford schools.
In the latest Ofsted reports, Orchard Meadow and Windale are deemed as requiring improvement while Pegasus was considered as good by inspectors.
Mr Coles said: “There is a great deal to admire about the three schools and we know how popular they are with local families.
“There are, of course, also areas for further improvement that the schools are ambitious to achieve.
“By being part of our group, they will be able to retain everything that is currently successful while accessing the sharing of expertise, best practice and operational management that our schools benefit from and that will help them drive up improvement at pace.”