While any enrolment zone would not impact on those students already enrolled at the school, it would have a future impact on who would be able to attend the school, the spokesman said.
The zone would be one of the terms negotiated in the Deal of Integration.
Earlier, Education Minister Hekia Parata had said that under integration the elite secondary school would now be open to a cross-section of students.
"Being integrated means that a more diverse cross-section of students can now attend the school," she said.
Before integration becomes effective from the end of January, a Deed of Integration would be negotiated with the Wanganui College Board of Trustees on behalf of the Minister, the spokesman said.
"This was required as part of the Private Schools Conditional Integration Act."
As an integrated school, the only compulsory fee for day students would now be attendance dues. The level of attendance dues was yet to be set, the spokesman said.
"But this will be discussed as part of the Deed of Integration. Boarding fees will still apply and the school will still seek donations. These will be determined by the board." It was expected that the Deed of Integration will be negotiated and signed before Christmas.
A new fee structure would be in place for term one of 2013, as the school would be integrated from that time and not a private school, the spokesman said.
Collegiate headmaster Tim Wilbur said even though he was relieved and pleased for the school and Wanganui, he was unable still to answer any questions.
"This is not obfuscation. The minister's decision means we now return to negotiation with the Ministry of Education to cross every 't' and dot every 'i' and I cannot pre-judge any outcome. The real work to create the new integrated Wanganui Collegiate School now begins," he said.
Meanwhile, Post Primary Teachers Association president Robin Duff said the decision to grant the Collegiate state integration was a case of Ms Parata robbing from the poor to give to the rich.
"The Government is so short of cash it can't afford to keep special schools open or provide extra staffing for low decile schools, yet it seems to have a spare $3 million to prop up ailing private school Wanganui Collegiate," he said.
"That Hekia Parata could possibly think she is helping our most vulnerable by pouring millions into a school that serves society's privileged defies belief. One would have to question whether she has actually lost the plot," he said.