Lindum constructed a new £1.6m science block at University Academy Holbeach.
The building, made up of four laboratories, two classrooms, three offices and a toilet block, was completed in November 2020.
The extra room will allow the school to accommodate an anticipated growth in student numbers.
The building work was carried out by Lindum Peterborough and was completed in 44 weeks.
Senior Construction Manager Colin Knight said it had been an incredibly smooth project.
“The new block has been built on part of the playground and we have managed the entire process, from foundations to steel structure to appointing a specialist furniture contractor for the fit out,” he said.
“When we started work, the school was fully occupied but obviously that changed when the country went into lockdown. By the time the pupils came back in September, the building was almost complete.
“We worked with the client to shuffle the construction programme and get the Tarmac laid earlier, which allowed us to make it safer for pupils while we finished off.
“Overall, the project has gone really well and we’ve developed a great relationship with the client.”
University Academy Holbeach is part of the Lincolnshire Education Trust, which is a family of schools supported by the University of Lincoln.
Previously, UAH had capacity for 1,350 students and sixth-formers across Years 7 to 13 but following a request from Lincolnshire County Council, it made room for an extra 60 Year 7 students from September 2020, taking its total register up to 1,650 places.
In a joint letter to parents, carers and staff, UAH executive principal Steve Baragwanath and Andrew Breckon, chief executive officer for the Lincolnshire Education Trust, the school’s trustees since 2011, described the expansion as a way to “avoid having to turn future pupils away”.