Hutt Valley High School has isolated eight of its classrooms after high levels of mould were identified during renovations to its roof.
Kim Shannon, head of Education Infrastructure Service, told Newshub the Ministry of Education was made aware of the mould last week.
“During roofing and refurbishment work being carried out on Block C, air testing inside the building identified unsafe levels of mould.
"Eight teaching spaces have now been isolated and some students are taking their lessons in the hall."
A senior student, who wished to remain anonymous, says he fears the mould could send him and his peers back to online learning.
He told Newshub students are struggling to focus and keep warm after being moved into the "cold" hall.
"No class has an independent space for the teacher to teach, instead, we now have to deal with competitiveness."
An email, shared with Newshub, outlines the school and their senior leadership team are considering remote learning.
"The health and safety of everyone on our site is the top priority," reads the email from acting principal Denise Johnson.
"We are working closely with both the Ministry of Education and our contractors to understand longer-term implications. This includes investigating contingency plans to ensure we minimise the impact on teaching and learning."
The student and his classmates were hopeful last year would be the last of online learning.
"It's horrible because we had to deal with that last year and I don't think it's good for students to learn online."
He says a teacher told him mould had been an issue for 26 years.
"It's been a really pressing issue, I've only come to the knowledge of this as it has gotten progressively worse."
Another teacher close to the student told him a colleague with autoimmune disease was being affected by the mouldy environment.
"Her immune system was affected due to working in that space."
The senior student told Newshub the block of classrooms affected is largely an English department - and the mould spreads like wildfire on paper.
"It's an English department, there's always paper everywhere and we've had to chuck all that stuff out."
The Ministry of Education has commissioned further air testing and expect results in the coming days - results the school of 1700 is anxiously awaiting.
Hutt Valley High School has been approached by Newshub for comment.