Dysart School, in Ewell Road, had applied to Kingston Council to build a post-16 educational building using a £1,000,250 grant from the Education Funding Agency.
Councillors agreed the expansion plans at the development control committee meeting on Thursday, February 26.
The new building will be built on playing fields at the back of the school site, on land owned by Kingston Council and shared with St Matthew’s Primary School, in Langley Road.