Scientists and some principals are questioning why masks are not mandatory when students return to school on Thursday under the new-look COVID-19 alert level 2.
Overseas it's the norm to wear masks in schools, but in New Zealand the Director-General of Health Dr Ashley Bloomfield says "it's a recommendation, not a requirement" for secondary school students.
Epidemiologists like Otago University's Wellington-based Dr Amanda Kvalsvig say they've been pushing for mandatory masks in schools since April 2020.
"It's frustrating that so late in this pandemic we are still discussing the evidence around masks in schools," she said. "They add one more layer to that swiss cheese of protection against COVID-19."
Principals Federation president Perry Rush is also questioning why face coverings are not compulsory when students head back to class.
"It is recommended internationally and given that students are in close proximity in classes, it makes sense in secondary schools."
Research suggests Delta thrives in older, poorly ventilated buildings like some classrooms.
PPTA president Melanie Webber says some teachers will be worried about going back to schools.
She says some will wear masks to model good behaviour to their students, but others will feel uncomfortable wearing one all day.
"It's good to have guidelines which will make students feel they can do it."
Offshore, teachers have borne the brunt of the mask debate, some have been attacked for trying to enforce it.
It's mandatory in the US for secondary-age children to mask up in school, but states Texas, Arkansas and Arizona are challenging the rule.
In Scotland, masks in class are mandatory, until the end of September at least.
Britain and Wales no longer require them except on school buses - instead regular mass testing ensures everyone entering class is COVID-negative.
Epidemiologists in New Zealand say testing at the gate could be a possibility one day, but until then, donning a mask in class should be a no brainer if you feel comfortable to do so.
"We really don't want our children to become unwell and that means adding in extra precautions until children are vaccinated, and we have better testing," says Dr Kvalsvig.