Education Minister Hekia Parata says the Government has no plans to back down on its controversial policy under which some class sizes will increase.
The largest school sector groups have united in opposition against the plan and are calling for an urgent meeting with the minister.
In May, the Government announced in the Budget it is setting new teacher-pupil ratios in schools which will result in some schools losing teaching positions, as well as cuts in technology funding.
From 2013, student ratios for Year 2 to Year 10 will be standardised at one teacher for every 27.5 students, an increase of four students for some classes.
Professional associations representing primary, secondary and intermediate school principals, the School Trustees Association, and the unions representing primary and secondary teachers and principals met on Tuesday and agreed that the Government's policy is unacceptable.
Educational Institute president Ian Leckie says the groups did acknowledge the current economic climate that prompted the Government to seek savings from its education spending.
"We also agreed that the Government's Budget announcements, including increases in class sizes, are educationally flawed, contrary to the best interests of students and are collectively rejected by teachers, principals and boards of trustees."
The groups say their joint statement calling on the Government to scrap its policy is unprecedented and an indication of just how seriously they take the issue.
However, they say it is too early to discuss what action they might take if the Government ignores them.
The Education Minister said on Tuesday the focus of the policy is on quality teaching and, though the Government is listening to parents' concerns, it intends to forge ahead.
Hekia Parata says she will meet with each sector organisation individually later this week.