Parents will have to keep finding extra cash if they want their children to have a rich education, Christchurch principals say.
Throughout the year, parents are asked to pay for more stationery, field trips, camps, swimming lessons and other extra-curricular activities.
Stationery lists have become more extensive, with parents having to supply whiteboard markers, glue sticks and scissors.
The costs are in addition to the school donation parents are encouraged to pay.
New Zealand Principals' Federation president Phil Harding said schools often asked parents to pay for extras during the school year.
He said the law was confusing, but politicians had no appetite to change it. "At the end of the day, teachers are not sitting there trying to rip people off and getting parents to buy whiteboard markers to look at. They are doing this in good faith because they think they need them."
Going on camps was technically part of the curriculum and the Government said the curriculum was free, but without parents' help to pay for camps they would not happen, Harding said.
"We tread a fine line between 'the curriculum is free' and 'please make a contribution'."
If parents refused to pay, there was a risk schools would stop providing the extras and say "no" to visiting performers and organising swimming lessons.
"These things are all part of a rich education," Harding said.
Cashmere Primary School principal Jacqui Duncan said there was an expectation from the community that the school would provide as many opportunities as it could for pupils, and that came at a cost to parents.
"When you say education is free, it gives the view that there is no cost, but the cost of running a school is huge. People need to realise that and need to value the very good deal they get for what is in most cases a few hundred dollars a year."
Canterbury Primary Principals' Association president John Bangma said schools never had enough money to do everything they wanted to do.
At his school, Mairehau Primary, if a parent could not afford their child attending an event that was an integral part of the curriculum, the school would pay for that child to attend.
Cashmere High School principal Mark Wilson said if pupils decided to do additional activities, he did not have a problem with parents paying the additional cost.
"Schools are not resourced to provide additional activities."
West Spreydon School principal Marriene Langton said the school asked parents for money only when it had to, and it tried to keep excursions to a minimum. The school tried to give lots of notice and it had a hardship fund.
Stocking up helps to reduce big school costs
With three children at school it does not take long for Sacha Sayers' wallet to empty when the school asks for money.
"I just seem to be shelling out $2 here and $5 there and for extra stationery. It does add up throughout the year."
However, the Christchurch mum does not want her daughters, Autumn, 9, Kendal, 7, and Eve, 5, to miss out on school outings.
She has no problem in paying the money. Who else would if parents refused, she said.
If the Government paid schools extra to provide those additional activities people would end up paying for it through increased taxes, she said.
One of her girls has a school camp this year, which is $200, but the West Spreydon School gives parents plenty of notice and allows parents to pay things off.
Sayers said she would also have to pay for swimming lessons this year, but they were subsidised and were much cheaper than if she had to pay the pool directly.
To cut down on back-to-school costs, Sayers buys stationery including whiteboard markers and gluesticks by the box load when they are on special throughout the year.
At the beginning of this school year she only had to pay $20 for the girls' stationery - it would have been $100 - because she had stocked up throughout the year, she said.