Schools are splitting classes up and sending students home as they struggle to find enough relief teachers to cover staff sickness.
One principal says there is a "definite shortage" of relief teachers, and with winter sicknesses and Covid-19, the situation is proving "pretty insurmountable" for many schools.
On Thursday, Mt Cook School in central Wellington asked parents not to send their children to school because half its teachers were off sick with Covid.
Principal/tumuaki Adrianne McAllister said the school had managed to stay open so far this week by combining classes and having senior leaders teaching instead.
"Today, everyone was just falling down sick," she said.
"Normally we have enough relief teachers at our school, but it was a combination of so many of our staff were away, so many of our support staff are away, so we have to just make sure everyone is safe and have enough staff to cover that."
Wellington Regional Primary Principals' Association president Nigel Frater, who is also the principal of Plateau School in Upper Hutt, said the problem had been building, particularly over the last few weeks.
"I've noticed it in my school ... it seems there is a bit of a pattern. Other schools are reporting issues around staff sickness and trying to find relievers - really difficult at the moment," he said.
"The situation's been difficult for a while but it's certainly now with these winter sicknesses and Covid presenting it's proving pretty insurmountable for many schools.
"For example you might end up with two or three classes in the school hall with one person taking them, I've seen examples of that recently; splitting classes up, which is when a teacher is off and you can't find a reliever so you have to spread your kids out across the school and other classes.
"That's not ideal either for the classes and teachers they're going into but also for the students as well, obviously their normal programme is detrimental as a result."
Frater said asking students to stay home was a last resort, but was not completely unheard of - he had done the same when his school could not find enough staff.
"Kids belong in school, but if you can't staff your school to the required levels then that's an option," he said.
"We have the children's interests at heart when these sorts of things happen, we work from that perspective - I think I would speak for all schools and principals when I say that."
Relief teachers in Wellington were "very, very thin on the ground", Frater said, while Auckland was struggling with longer-term vacancies.
"I think just in general there is a definite shortage of teachers, certainly in specific areas," he said.
"Many relief teachers are getting steady work in schools and don't feel that they need to put out for day-to-day relieving which is where you might get called in the morning when a teacher is sick ... you might be able to get, for example, two days a week at a school and that will be sufficient, you don't need to really go outside of that."
The demand for primary-level relief teachers might also have increased as a result of the collective agreement inked last year, which saw classroom release times increase from 10 to 25 hours per term, Frater said.
At Mt Cook, the call to stay home was heeded on Thursday with only about 50 of the school's 264 students attending, and some parents offering to look after friends' children.
"I didn't want to shut the school down because I know parents work and need this, so it was just about reaching out to our community and they all helped each other and we've managed to get through today," McAllister said.
The school had secured enough staff for Friday, but McAllister said it was anyone's guess as to whether the situation would be repeated.
"We're just day-to-day at the moment, because we've had another couple of staff go home today feeling unwell and one's tested positive."