Parents are raising more than $357 million a year in donations and fundraising to support the "free" schooling system.
Schools in wealthier neighbourhoods are bringing in an average of $740 a student each year in donations and fundraising, figures released to the Weekend Herald show.
The amount raked in by voluntary donations has climbed - but so, too, has the millions of dollars brought in through increasingly sophisticated fundraising drives.
School fairs at some Auckland primary schools have developed from baking and coconut shys to include silent auctions for donated items including overseas holidays, with the most successful bringing in more than $100,000.
Others are targeting ex-pupils for ongoing support, something traditionally associated with the tertiary sector.
According to information released to the Weekend Herald, the amount of voluntary school donations, contributions and fundraising received by state and state-integrated schools was $357.54 million in 2012, the most recent figure available. That was an increase of more than $16 million from 2011.
One parent with two children at a state primary school has questioned the more than $1000-a-year cost. The mother, who asked not to be named, paid two lots of the $480 donation at Auckland's decile 10 Meadowbank School, and then an additional $167 in activity fees.
"If you don't pay your donation or you part-pay, your child gets an envelope to bring home about once a term to ask for payment - i.e. they are named and shamed."
Meadowbank principal Peter Ayson said the donation was determined by the board of trustees and in line with other schools in the area, and the amount asked for at Auckland schools tended to be higher.
Around 85 per cent of families paid, and no pressure or action was taken against those that did not, as the school recognised they could not afford to.
The overall figures also showed a marked difference between what schools in poor and rich areas took in fundraising. In 2012, decile 10 schools brought in an average of $445 more per student in fundraising and donations than their decile 1 counterparts.
Principals' Federation president Phil Harding said the imbalance was somewhat addressed by more government funding given to lower decile schools, but that was not so much the case for mid-decile schools.
He said he believed that in recent years it was understood that a donation was just that.
Labour education spokesman Chris Hipkins said parents had always willingly contributed to some of the optional extras, "but increasingly they are now being asked to pay for the basics".
"What we have seen over quite a sustained period of time is an erosion of school funding in real terms relative to the costs that they face."
Education Minister Hekia Parata said schools' operational grants had been increased by more than $500 million over the past five years - increases that, on average, had kept pace with inflation and allowed schools to keep up with real costs.
"Despite tight fiscal times, we put more than $9.7 billion into education in 2013-14, the highest spending ever in education."
Ms Parata said donations were not compulsory, and boards of trustees decided upon what parents were asked for. "That's up to each school and their parents. They need to be talking about those expectations."
