The head of primary school teacher union NZEI TE Riu Roa says today's strike action across the country is a symptom of underfunding in the sector.
Teachers are preparing for a full-day strike today for the first time in 24 years over a pay rise and a bid for smaller class sizes.
The union says that means 27,745 teachers and 1827 principals won't be at work.
Union head Lynda Stuart, speaking this morning to TVNZ 1's Breakfast, said there is a real struggle to attract people into teaching, and to keep them there.
"We're really struggling within education at the moment with primary teaching and secondary teaching," Ms Stuart said.
"People have got lots of options when they leave school ... they can go into all sorts of different things and teaching just isn't attracting them.
"This is a symptom of underfunding.
"We're marching across this country because our kids are that important to us."
The union is seeking a 16 per cent pay rise across the board, she said, as well as smaller class sizes and more support available for teachers to deal with challenging students or those with learning difficulties.
Offers made by the government were unacceptable for more experienced teachers, she said.
"For those people at the top end of the scale it's certainly not a significant enough shift," Ms Stuart said.
"They have huge experience in the classroom and we want to acknowledge that moving forward ... we want a significant pay jolt for everyone."
Ms Stuart said the decision to strike now, after a wave of industrial actions by other unions this year, was not to do with the Labour Government coming into power.
She said teachers had numerous "fights" with the National government over issues like national standards and class sizes, and that it was simply the right time.
"This was going to have to happen," she said.
"When you are government it is your responsibility to fix what you see in front of you ... and it's time to fix this."
"We're really clear about the solutions we bring to the table for negotiation."
The Ministry of Education has said it values the work of principals and teacher immensely, and that reaching a settlement is a priority, but also that they are disappointed with the action.
Spokesperson Ellen MacGregor-Reid said "we are disappointed the union has decided to take strike action while we are still in the negotiating process".
"Both parties wish to explore every possible avenue to reach an agreement ... we will continue to negotiate in good faith," Ms MacGregor-Reid said.