Work on a new school in Swanage will start earlier than planned after councillors gave the the go-ahead.
Dorset County Council's cabinet gave permission for The Swanage School to start work on the existing Swanage Middle School site in February - six months earlier than was planned.
Disruption to Middle School pupils must be kept to a mimumun, while Swanage Town Council must give up land on Northbrook Road to relocate St Mary's RC Primary School.
Cllr Toni Coombs, Dorset County Council cabinet member for children's services said: "This is an extremely complex and sensitive issue, linked with the wider Purbeck schools reorganisation.
"Any delays here will substantially increase costs and affect the money available for other aspects for the reorganisation, including the proposed new primary school in Bere Regis.
It was originally agreed by Dorset County Council that no major construction work would take place on middle school sites during term time.
However, The Swanage School asked to begin work in February - to avoid the creation of a temporary school.
Cllr Coombs added: "We have balanced the competing views and needs of the local area and have agreed a way forward that is in the best interests of local children across Purbeck.
"It will ensure the Purbeck schools reorganisation remains on track and within budget."