Christchurch Girls' High School will get a new main block after five years of trying to strengthen the existing one.
Thousands of students have been taught in the quake-damaged, then partially-finished, block at the decile-10 state school since the 2011 earthquake.
The ministry was told by consultants in 2015 it would cost much less to rebuild it entirely, and the school board has pushed since then for such a rebuild well away from the less stable land by the Avon River occupied by the existing block.
Instead, the ministry spent about $7 million on strengthening it before work ground to a halt in the last two years, due to cost blowouts and disruption to classes.
The ministry had told RNZ it spent $5.4 million on construction, however this did not take into account another $2.1 million of other costs connected to the main block and revealed in an OIA response.
In a newsletter to families, principal Christine O'Neill said the ministry had confirmed a rebuild last week.
"New buildings will deliver us the best long-term facilities and minimise disruption to teaching and learning," she said.
"We have been in regular contact with the ministry through this process and fully support this solution."
Former board chair Mike Lay earlier accused the ministry of covering up a waste of taxpayers' money and time spent pursuing the wrong option against expert advice, and retaliating against him when he questioned officials.
The school's technology block will also be replaced, and an art block refurbished.
Construction is likely to start in late 2022, just prior to when the whole city-wide school rebuild programme was meant to wrap up in 2023.
"There will be significant planning and design work that needs to take place before we get to the construction phase," O'Neill said.
"We will be working with the ministry in the new year to identify a design team for the project and we will work closely with both them and the ministry to ensure we deliver the best possible outcome for our school and community."
