Oldfield School at Newbridge in Bath has been granted planning permission for an extension that will significantly improve teaching facilities.
Bath & North East Somerset Council planners have approved a new two-storey teaching block at the secondary academy on Kelston Road.
The 1,243-pupil school falls within the Green Belt.
The new building will be on scrub and grassland at the rear of the dance studio and science block.
There will be two classrooms for design and technology including a food technology kitchen/classroom and science labs.
The school says at present it does not have suitable classroom facilities to accommodate all design technology, food technology and science lessons.
The result of the overcrowding and shortfall issue is that, for example, science lessons are taught in classrooms where there is no access to equipment and infrastructure, such as Bunsen burners.
Food technology teaching also has very specific equipment needs, such as food preparation and cooking facilities, which are not transferrable between classrooms.
There has been concern that these shortcomings could harm pupil attainment and Ofsted ratings.