Work on Morriston Comprehensive School's new £3 million science and maths block is on course to open in September.
Swansea Council said most of the building's steel frame is finished and work is progressing on the ground floor brick-work.
When finished, the two-storey extension will house dedicated classrooms for maths teaching and hi-tech science laboratories.
The cash for the scheme is coming from the Assembly's school building improvement grant.
Head teacher Peter Washbrook said: "This investment at the school will have a positive impact on pupils and staff, and should provide an enormous contribution to our young people's studies."
