Plans for the £800,000 expansion of Redgate Junior School, in Hunstanton, are expected to be submitted in the next couple of months.
Norfolk County Council wants to add two new classrooms to the Collingwood Road site and transform an existing area into an additional third classroom.
The work is planned in advance of the amalgamation with Hunstanton Infant School in September next year.
A council spokesman said a decision on what will happen to the infant school site, in James Street, is yet to be made.
The proposed enlarged Redgate School will take the infant school’s 90 pupils and have capacity for 210 pupils in total.
The spokesman said: “We are proposing building a two classroom extension and transforming an existing space into a third classroom. There are also plans for new toilets and outdoor space for the younger children.
“The plan is for the building to be ready for the changes in 2015 and we will be submitting a planning application in the next couple of months.
“We have set aside £800,000 for the project.”
The schools have shared a headteacher and governing body since September 2009.
Plans to amalgamate the schools were approved in April following a consultation with parents.
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