North Otago Primary Principals Association chairman Brent Godfery said teachers were being forced to come in sick because of a lack of relievers.
The situation also meant parents were being asked to keep their children at home and some teachers were having to look after two classrooms to cover for absent colleagues.
He feared the situation was about to get worse as winter fast approached and called on the government to properly invest in teachers.
Mr Godfery said he already had a day this year when he asked parents to keep children at home and last year there were four.
"Once last year I had 14 of my 30 staff away on one day and and we asked the whole school to stay home and only send your children if you have to.
"We ended up with 40 children out of 250 who came to school and the rest of the parents were very supportive and kept them at home that day."
He said the government needed to prioritise getting a bigger workforce of teachers.
"They’re putting investment into stuff that I don’t think is necessary ... and they’re cutting things that they should not be cutting."
"People are just scraping through at the moment and it makes me annoyed that there aren’t enough teachers around and people are choosing to leave the country."
He said he knew of three teachers personally who had gone to Australia for better pay where they could earn about $20,000 more than they did in New Zealand.
Bracing for the winter, when illness was expected to rise, there was not much that could be done, he said.
"At this stage we just have to keep our fingers crossed."
Mr Godfery said some schools were paying for teachers to get the influenza vaccine to lower sickness and teachers would try their best to make it to school when they were sick.
"Teachers are good at not looking after themselves because their attitude is the kids have to come first.
"I’ve got a teacher at school today who should be home."
