Principal Steve Hall said the buildings would be needed for the next 18 months as the school’s capacity was increased from 1200 pupils to 1800.
They consisted of 18 new "state-of-the-art" teaching spaces, as well as work areas for staff.
"It’s been a push to get them ready on time, but the quality of them is fantastic," Mr Hall said.
They were housing the maths and languages departments, as well as some other classes, and were configured for a range of spaces that could have either one, two or three classes together at a time.
The teaching areas replaced those lost at the eastern end of its three-year-old building, where two two-storey wings are being added.
The school was also losing access to its technology and performing arts areas while internal modifications were being carried out.
The extensions were originally scheduled for completion by the middle of next year, but had been delayed by six months.
The work, which would also double the size of the gymnasium, would be completed in stages throughout next year. The internal modifications would be completed on the technology area by the end of this year, and to the performing arts area by the end of first term next year.
Mr Hall said the school was undergoing a lot of change over the next 18 months, but it had a "track record of doing pretty well during those times".
"And it’s going to be amazing when it’s done."
He would not have an accurate number for the school’s roll until next week.
