Cultural problems at a Sydney high school have been cited as partly to blame for what a parliamentary inquiry has been told was an asbestos "cover up" at the campus.
The NSW upper house inquiry is probing the presence of asbestos at Castle Hill High School, with members of the school community including teachers, parents, and students invited to provide submissions.
The inquiry on Monday into the north-west Sydney school is taking place six years after the potentially lethal material was reportedly found on the grounds.
Teachers Shane Stubbs and John Connell told the inquiry of their experience at the school, with Mr Connell testifying that classes continued despite asbestos being found in ceilings.
Mr Connell said unlike a previous asbestos incident at Beverley Hills Girls High School in 1993, which caused that school to be closed, a decision was made to remediate the situation at Castle Hill "and allow the school to keep running".
"There's nowhere to send the kids at Castle Hill High anymore, all the other surrounding schools are also full," he said.
Mr Connell testified "a whole bunch of directors were told about" the issue and said he "never thought of the concept that they'd actually done a test and it had come back positive, and then told us it was negative".
Pauline Hanson's One Nation MP Mark Latham questioned why the former principal had remained in charge "and how was the school still open".
Labor's Anthony D'Adam pointed to "systemic failures" and "fundamental cultural problems" at the school.
"(It's) around principals being incentivised to keep a wrap on issues that are brewing in schools," he said, calling schools a "black box" and principals the "choke point" on information flows.
Labor MP Courtney Houssos described the teachers' evidence as "shocking".
"I think that the scale of the cover up has been deeply, deeply disturbing and I thank you for your frank testimony," she said.
Earlier this year, Castle Hill MP Ray Williams told parliament that in 2016 the school community was told an asbestos test was negative when it was in fact positive - a hidden outcome that had put thousands of people at risk.
Mr Williams, school parents and education department officials will give evidence at the inquiry later on Monday.