Monitoring carbon dioxide levels isn't just a good way to measure Covid risk in the classroom - one Auckland school had found it is also an excellent way to learn science and maths.
Students at Glen Taylor School in Glendowie have been checking out the freshness of the air around their school, from the middle of the field to the back seat of a crowded car.
They've been using portable Aranet carbon dioxide (C02) monitors, which are being provided by the Ministry of Education to all schools in New Zealand.
Low CO2 levels mean a room is well-ventilated, so the coronavirus can't build up in the air.
The US Centres for Disease Control advises a well-ventilated room should have CO2 levels below 800 parts per million.
The students found in the middle of the school field, C02 was 413ppm; even in a full classroom with doors and windows open it only climbed to 494ppm.
However, when the class crowded into the principal's office, it climbed to more than 1000ppm within five minutes.
Soane Savieti,12, was among six Year 8 students who piled into a car with the windows up. Within 5 minutes, the reading had climbed to 5010ppm, he said.
"Once we got out of the car my legs were wet from sweat."
High levels of carbon dioxide could mean students got dizzy or found it harder to breathe, he said.
In a classroom with windows open, CO2 measured at 494ppm. With the windows closed and 1m social distancing, it rose to 595 within five minutes.
Soane said the classroom windows were always left wide open now; when it was cold the students just wore extra clothes.
Principal Chris Herlihy said students had got right into the experiment, looking at the science of breathing and the dangers of high CO2.
"They've been comparing and contrasting the numbers, looking at what's a safe environment and what's not a safe environment."
Herlihy had been struck by the effects of excess CO2 on students' learning, even if nobody had Covid.
"Anything over 1000[ppm] they're saying your brain functionality reduces by 15 per cent. Anything over 1400 your brain functionality reduces by 25 per cent," he said.
"Now they've got the science in behind it, it makes them feel a bit safer in coming to school."
All New Zealand's 2500 schools should have received a portable CO2 monitor, so they can test the air in different learning spaces to see if change is needed.
The Ministry of Education has also ordered 5000 air purifiers for schools, and is seeking suppliers for another 5000 over the next two years.
But it says for most of New Zealand's 35,000 teaching spaces, opening doors and windows remains the best way to keep the air fresh and the virus from building up.
Starship paediatrician Dr Alison Leversha said the message used to be that Covid spread in droplets, which only travelled a short distance. But it was now known there is 100 times more virus in aerosols than in droplets.
Leversha has been visiting education facilities, spreading the message that Covid is airborne and will circulate over time to fill an enclosed space.
That means social distancing in badly ventilated classroom isn't much use as virus particles will still reach everyone eventually.
However, if the air students and staff breathe out is regularly replaced with fresh air from outside, virus particles will be flushed out the windows too.
At Glen Taylor, Herlihy is hoping they're past the worst of the Omicron outbreak. The number of cases in Auckland schools is trending steadily downwards and most other regions are also seeing a drop in numbers.
Half of the school had had to isolate this year as a case or a close contact, but attendance is now back up to 86 per cent, Herlihy said.
He believed monitoring CO2 levels - along with masking and practices like sending kids outside for regular breaks - helped give parents confidence to send their kids to school.
"We've been able to show people that if you open your doors and windows there is no issue - you're basically living in an outdoor environment."
The Herald visited Glen Taylor on a windy day with the breeze wafting through wide-open windows. In winter, it will be a different story - the rooms will be preheated and windows only left open a few centimetres.
Leversha said when a room had been heated, and it was cold outside, the difference between the two temperatures created airflow.
"You're better to have a whole lot of windows open a [small] distance in winter and you should get good exchange. In fact you may get more fresh air in the winter than you would in the summer."
The Ministry of Education's ventilation team was doing further work before winter, but they currently believe windows may only need a 5cm opening to provide sufficient ventilation in the coldest months.
Some principals have raised concerns that in the winter months that won't work, especially in the deep South where it will be too cold to open windows.
The ministry has acknowledged that's an issue and says when it allocates air purifiers, it will prioritise schools with added challenges including low vaccination rates, lower decile areas and those in colder or variable climates.