Some school principals say new Government policy on class sizes will make learning more difficult for struggling students.
In a pre-Budget speech, Education Minister Hekia Parata said the Government will increase school and early childhood education spending by $511.9 million over four years in next week's Budget.
Wednesday's announcement also included changes which will lead to larger classes in the middle years of schooling.
Class sizes will increase for Year 2 and Year 3 but decrease for Years 4,5 and 6 under changes to the funding formula used to determine the number of teachers at each school.
Island Bay School principal Perry Rush says his Wellington school is likely to lose at least one teacher.
He says this means several classes will have to take on more pupils, which is a concern given the growing number of children with additional needs.
The principal of Christchurch's Mairehau Primary School, John Bangma, says his school may have to cut back on reading recovery programmes.
Mr Bagma, also president of the Canterbury Primary Principals Association, says larger classes will also prevent many children getting the extra attention they need following the Canterbury earthquakes.
NZEI president Ian Leckie told Morning Report that parents should be very worried about the changes.
But Hekia Parata told the programme class sizes will not necessarily go up at every school, and said the primary teachers' union is scaremongering about the changes.
She said it would be up to principals to decide how resources will be used to best meet the demands of the rolls at their school.
Ms Parata has said the Government would save on average $43 million a year over the next four years by changing the ratios used to decide how many teachers are funded at each school.
She said the Government is not reducing the number of teachers it pays for, but controlling the growth of that number.
However, teacher and principal groups have said the changes could cost between 400 and 500 jobs.