Perryfields High School, in Oldbury, now has enough classrooms for their 1200 students.
It was promised £18.5 million as part of the Building Schools for the Future scheme.
With that money, it planned to build a new teaching block and restore old ones.
But, that scheme was scrapped last year.
The school was originally built for 550 pupils in the 1950s but with more than 1200 students attending the school in 2012, they had to hire 4 mobile classrooms to accommodate their increasing numbers.
Earlier this year Perryfields borrowed £1million from Sandwell Council to build 28 new classrooms.
Most of the building work took place over the summer holiday, taking 22 weeks, and now students are learning in the new rooms.
The school also used some the money to landscape a multi use games area for pupils to play sport and relax. This is on the ground where the old porter cabin classrooms used to be.
They were only meant to be a temporary measure but had been in place for 25 years.