Kiwi parents have contributed nearly $1 billion in voluntary donations to schools since 2000.
Figures released to ONE News show New Zealand schools received $70 million in donations during 2014, with the total over the past 15 years at $950 million.
"Schools are really caught between a rock and a hard place," Labour Party education spokesman Chris Hipkins said.
"Government funding is simply not keeping up, if they’re not getting the money from government they have to get it from somewhere else so they’re resorting to asking parents to pay more and more of the cost of their kids’ education."
The New Zealand taxpayer contributes $100 to schools for every $1.80 donated privately.
Education Minister Hekia Parata also says the Government plans to spend $11 billion on early childhood, primary, and secondary education this year.
The figure is more than the budget for the police, defence force, roads, and foreign affairs combined.
However, the Post Primary Teachers Association wants the Ministry of Education to investigate how much it costs to run a school.
"This is about what is needed to provide safe, warm, and clean classrooms. It's about providing sufficient resources for the teachers and the students," the PPTA’s Angela Roberts said.