O'Connor said if the school was not able to ask parents to help pay for their children to go on camps, it would "put huge pressure" on the school's Board of Trustees to meet the costs.
Children in year 5 and 6 attended camps, which were part of the curriculum and provided valuable experience, O'Connor said.
"For some children, it is the first time they will spend a night away from home and it is a very important developmental experience for them."
Attending camp is like a badge of honour for attaining seniority and it would be devastating if they had to be cancelled she said.
Education Minister Chris Hipkins has said the law governing what is classed as a "donation" was not affected by the offer of the $150 grant.
"If schools choose to opt into the donations replacement scheme, they will no longer be able to request any parental donations," he said.
"Schools that choose not to opt into the scheme can continue to ask for donations as they do now."
Just as attending camp is a right of passage for primary students, school balls are a celebration of seniority for high school students, although not part of the curriculum.
Some New Zealand schools have told students they cannot purchase ball tickets if their parents are not up to date with "voluntary donations."
"Ball tickets are a separate, user-pays cost and we would never penalise a student in that way," said Whanganui City College deputy principal Val Rooderkerk.
"We combine the school ball with the leavers' dinner, which is better for parents and for students because it all happens at the end of the year so it's less expensive for parents and students can focus on their studies."
While both Rooderkerk and O'Connor welcome the Government's moves to ease financial burdens for parents, they hope that students will not miss out on valuable activities as a result of the reforms.
"I am cautious about my comments at this stage because I think the full implications of the new grant are still sinking in," said O'Connor.
