The cost of repairing Avonside Girls' High School looks set to blow out to more than $20 million.
The Ministry of Education is expecting to foot a bill of $100 to $150 million to repair the school network in Canterbury.
This includes state schools in the Christchurch, Selwyn and Waimakariri areas.
A Ministry spokesman Jerome Sheppard said the final cost of repairs to Avonside will be dependent on the long term solution but estimated it would exceed $20 million.
Avonside was the most severely damaged state school in the February 22 earthquake with two large blocks having to be demolished. It has been site sharing with Burnside High School but returns to the school site at the beginning of the 2012 school year.