The job includes construction of a single-storey school at Link Road, comprising nine standard classrooms, a further two for early years learning and a glass atrium, which will supply light to a large shared learning area.
A garden courtyard, nature pond, hard play area and a netball court will also be provided under the deal.
Once the new school is built, the former 1960s buildings will be demolished, to make way for more landscape features and a football pitch.
Morgan Ashurst is one of seven construction partners delivering the seven-year education building programme, worth a total of £200 million, on behalf of Cambridgeshire County Council.
The firm is also building a £2.5 million extension to Lantern School in Ely – which will see its capacity increase by 50 per cent.
Bellbird School is due to be completed in March 2010.