Teachers are expected to vote in favour of an active campaign aimed at reducing class sizes - which could eventually end in industrial action if the Government does not listen.
More than 130 teachers are expected to gather in Wellington today for the annual PPTA conference which will look at a range of issues, including class sizes and whether the number of students should be capped.
A report that will be presented today and voted on during the conference recommends teachers "note with dismay the Government's failure to resource and introduce class size limits in secondary and area schools".
It also recommends PPTA's executive "continue to seek class size limits" through four mechanisms, including a campaign to raise public awareness, political campaigns in the election buildup and reintroducing the issue in the next pay negotiations.
The report warns that industrial action may be needed in order to get the point across at the negotiation stage.
PPTA president Robin Duff said teachers had been fighting to introduce class size limits for more than a decade but had struggled to gain traction, mostly because of the financial costs of implementing such a change.
PPTA executive member Angela Roberts, who is presenting the class-sizes paper, said the number of students in classes varied greatly from school to school but a recent survey found one class had 51 students.
Although the vast majority of classes were far smaller than that she said it was not uncommon for some to have up to 40 students, especially in larger schools.
Ms Roberts said it was up to conference members to decide on the exact figure they'd like to see classes capped at but most teachers saw about 25 as optimal.
The issue of capping class sizes was raised during last year's contact negotiations when PPTA asked for a maximum of 30 students per class and an additional 700 fulltime teachers to make that happen.
The ministry said it did not believe that bargaining was the appropriate place to negotiate class size and instead agreed to establish the cross-sector Secondary Schools Staffing Group which is now looking at the issue.
Part of the group's work involves developing case studies of how principals and boards manage class size and teacher numbers.
The group is due to report to the Secretary for Education early in February.
Education Minister Anne Tolley, who is due to speak at the conference today, said she would not comment on the PPTA paper.
"But I can say that as part of the recent PPTA collective agreement we have formed a working group to look at class size, which includes PPTA, the Ministry, SPANZ, NZSTA and other school representatives.
"The evidence shows it is the quality of the teacher, not class size, which affects learning," she said.
"Schools make decisions on class sizes, and we need to provide more flexibility for principals on how they allocate teachers, as the ways in which students are taught change in our modern world."
A survey this year of 11,689 classes from 323 schools around the country found that 8 per cent of classes had more than 30 students.
Teachers said their biggest concern about having more than 30 students was the inability to provide adequate individual attention and feedback to pupils.