Unions claim a plan to help struggling school students could inadvertently hurt other children who need extra help.
Research shows schools will actually have less money under the Ministry of Education's plan according to the NZ Educational Institute.
The institute says funding for support staff and other costs such as the power bill and even the toilet paper comes out of the school's operations grant.
The NZEI says this year that budget was frozen and the union claims that means with inflation and the rising number of students schools are actually getting less money.
The union says its research shows a 0.5 percent per student cut in operational funding next year but the Education Ministry says that's wrong and they cannot see how the NZEI has come up with their numbers.
The ministry says operational funding has gone up by 15 percent over the last six years.
The latest increase - $12 million - will be targeted to 150,000 students who have been identified as being most at-risk of under achievement.
"We absolutely appreciate that's a good thing to do but not at the expense of the operations grant which actually provides support for all children," NZEI national president Louise Green says.
A review of the $11 billion spent on education is underway.