Lawyers representing Aorangi School's board say rebuilding the classrooms would have been affordable if Education Ministry staff hadn't muddled their calculations.
They were speaking on Wednesday at a judicial review of the decision making process that will see the Christchurch primary school, attended by now Prime Minister John Key, closed.
In November Education Minister Anne Tolley cancelled plans to upgrade the Christchurch primary school, instead deciding to close it next month.
The board requested a judicial review, which is happening before Justice French in the High Court at Christchurch.
Much of the board's case is based on what its lawyers say was a flawed consultation process by the ministry.
They claim this included withholding the information which recommendations to the minister were based on, affecting the board's ability to provide relevant contrary data.
The board says the consultation carried out by ministry staff did not meet legal requirements, the school was treated unfairly and the decision is unreasonable.
Its lawyers told the court the ministry had never conceded that rebuilding the classrooms would have been achievable if it had got its figures right.
Lawyers representing the Minister will present their submissions on Thursday.