Pupils laid the first bricks in a £1.3m development at their Abingdon school.
Building work has started at Caldecott Primary on a new single storey building which will contain six classrooms.
The school is divided into two buildings, but the extension will mean that the school will be under one roof.
Part of the new area will be specially built for foundation stage children aged between three and five.
The modernisation will include a new library, reception area and the latest learning facilities.
Headteacher Margaret Gibb said: "We are confident that with our new building we will be providing the very best learning facilities in the area.
"It was exciting to see the children involved in laying the first bricks.
"We will follow the project through and are looking forward to watching the work progress."
The Caldecott Primary School project is part of a major re-development of the site.
A new £500,000 family centre is to be built there starting next Easter and part of the site will be sold for housing.
The money raised will go towards consolidating the Kingfisher special needs school on a single site in Radley Road Abingdon.
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