Schools will be more reliant than ever on parents' donations and fees this year, education leaders say.
They say many schools are getting minimal increases to their operational funding and will have to make cuts or put pressure on parents to pay voluntary donations.
This year, the government is spending 1 percent more on the school operations grant, the same increase as last year but about half the size of previous years' rises.
It is targeting this year's increase to at-risk children and some schools will get only a little of the $12.3 million available.
The government said only 15 schools would get nothing from the targeted funding, but 1582 others would receive somewhere between zero and $5000.
The president of the Principals' Federation, Whetu Cormack, said schools could not demand or require donations, but were likely to put more pressure on parents to pay them.
"My belief is that schools will be forced to put pressure on families to help increase their operations grant," he said.
Educational Institute president Lynda Stuart said parents were already paying for a lot and some schools would simply opt to do less this year, rather than ask families to pay more.
"Schools are really careful around asking parents for more money and I know that my colleagues really have to think hard about that, so it means that some things just can't happen."
Ms Stuart said schools could not cut back their spending on things like power and heating, so staffing and resources would suffer.
"The only two areas that you have any discretion around in your budget are the people, so that's those people that you employ as teacher aides, support staff, and curriculum resources.
"So when there is a cut to the funding those are the only areas you can go to and those are the areas that directly impact on children's teaching and learning."
The president of the Secondary Principals' Association, Sandy Pasley, said some schools would find it harder to make ends meet, but she did not believe they would put more pressure on parents to pay donations.
"I don't think they'll put more pressure, but they will certainly be more reliant on parent donations and will certainly be hoping that parents support them," she said.
Ms Pasley said some schools might make cuts in their spending on things like library books and subsidies for school trips.
Burnside High School principal Phil Holstein said his school would ring-fence the funding increase for use with at-risk students, because that was what it was intended for.
He said that meant the school was getting no increase to its operational funding and it would be a little more reliant on the donations it received
"We're looking at other income streams as well. International fee-paying students is also for Burnside a very significant part of that, but we're looking at other options as well," Mr Holstein said.
Education Minister Hekia Parata said the targeting programme would help the students who were at greatest risk of under-achieving at school.
"I do not expect this approach will put more pressure on parents' finances because it is new money on top of what schools were already getting," she said.
Ms Parata said only 15 of the smallest schools would not get any money from the scheme and in total schools would get $1.3 billion in general operations grant funding this year.