The Government ignored advice from the Ministry of Education and Treasury that the private school Wanganui Collegiate should not become a state integrated school.
Radio New Zealand has obtained information under the Official Information Act that show the ministry told the Government that there were already 1400 empty places in secondary schools in the Wanganui-Rangitikei region and integration would hurt existing state secondary schools in the area.
Integration came with a funding increase from $800,000 a year to more than $3 million.
Education Minister Hekia Parata said last year the school had been working toward integration for more than two years and was one of the top performing schools in the region.
Green Party education spokeswoman Catherine Delahunty said the Government had more than tripled the amount of money it gave to the school while closing schools in Christchurch.
"It is yet another example of privileging the privileged while everyday New Zealanders suffer," she said.
"The decision to hand out more cash to Wanganui Collegiate is a slap in the face for Christchurch students, parents and teachers who are desperately trying to save the schools that helped them through the traumatic experiences of the last two and a half years."
In June last year Wanganui Collegiate boasted low class sizes in advertisements - after the Government ditched plans to make $43 million savings a year by increasing class sizes.
The school has faced financial strife since 1991 when it made the move to become co-educational and it sold the land and buildings that house St George's preparatory schools, valued at $3.1 million.
Last year there were 518 students over the two schools and this year fees will increase by more than 10 per cent. Outgoing Wanganui Collegiate chairperson Tam Jex-Blake wrote to parents in December last year saying they would have to pay more.
In 2011 then Education Minister Anne Tolley gave Wanganui Collegiate more than $800,000 in extra funding, while the school's application to become a state integrated school was negotiated.
At the time Wanganui Girls' College said there wasn't enough funding in the region to support the current regime of public schools.
- APNZBy Kate Shuttleworth @K8Shuttleworth Email Kate