The demand for relief teachers has come early this year as winter sicknesses - and Covid-19 - impact schools.
Schools have been forced to split classes or send students home as they struggle to find cover for unwell staff.
Last month, Mt Cook School in central Wellington asked parents to keep their children home because half of its teachers were off sick with Covid.
Wellington Regional Primary Principals' Association confirmed the problem had been building, particularly over the last few weeks, and other schools are finding it hard to get relievers, too.
New Zealand Relief Teachers' Association chairperson Sally Wallwork said it was not known how many relief teachers there were across the country, but demand had been rife.
Relief had been needed in Auckland and Wellington but she recently heard that Christchurch had also had huge demand for relievers to cover teachers with Covid.
Wallwork told Checkpoint in the last week, a central Auckland school had 12 teachers - a third of its school - off sick.
"It's a common occurrence across the country right now in the main cities."
Schools were having to split classes, which meant each class had more students in it, and in some cases, principals and deputy principals were going into the classroom to cover.
Wallwork said it was "way early" for such demand - as relievers were usually needed in July.
But Wallwork said schools would just have to make do for now.
Sending students who were sick to school would contribute to contaminating others - including relievers who were needed.
"it just makes the problem worse, I believe."