It was decided the school would get a new main block in 2020, after five years of trying to strengthen the existing one.
The ministry was told by consultants it would cost much less to rebuild it entirely in 2015.
Regional Infrastructure Manager, Simon Cruickshank says the redevelopment is part of the Christchurch School Rebuild programme - originally supposed to finish by 2020.
He says the project is currently in design and will move into construction by the end of the year.
