An urgent parliamentary inquiry into Redeemer Baptist School in Sydney's west was called in July following allegations stemming from a media investigation by 60 Minutes and Nine newspapers.
Set up in 1981, the private school now teaches 563 pre-kindergarten to year 12 students and acts as a homestay for international students.
About five per cent of students are members of the church's broader community who live and work with their families on school grounds in North Parramatta.
Alleged instances of sexual, physical, verbal, psychological, spiritual and financial abuse by the school were detailed to the education committee inquiry chaired by Greens MP Abigail Boyd on Monday.
A former church member and ex-student said she was sexually assaulted by an adult church member multiple times when she was in year 7.
After reporting the abuse, she alleged she was forced to demonstrate what had happened to her on her mother, before being berated for the clothing she was wearing at the time.
The woman claimed the abuse was handled by the church internally and her abuser was banned from playing the drums in the school and church ministry as punishment.
Another man, who was born into the church and also alleged sexual abuse, said he spent almost three years planning his 1992 escape.
"I was so naive about the world. You're told it's black, it's evil, God doesn't exist outside of Redeemer," he told the inquiry.
Any child protection-related allegation was reported to relevant external authorities and referred for independent investigation, Redeemer headmaster Russell Bailey said in a submission to the inquiry.
In the 45 years the school has been accredited and registered, Mr Bailey said it had never been in breach of its legal obligations.
Michael Jones, who left the church in July 2021, said he completed unpaid work for more than a decade, sometimes working until midnight for several days in a row.
He was one of multiple witnesses who said they were taken from their family homes and made to live in a house with a church elder and school principal Jonathan Cannon alongside up to 25 others.
After obtaining their Higher School Certificate, Redeemer students must complete a 13th year of schooling.
Carol Matthews, NSW secretary of the Independent Education Union, described it as "clearly exploitative".
"Year 13 is essentially a year of unpaid labour in which you can be required to do whatever the school wants," Ms Matthews said.
Redeemer is the only school in the state that does not employ staff and relies entirely on volunteers for core teaching duties, Ms Matthews said.
Church members work on school grounds from year 7, completing lawn mowing, construction work and building maintenance, with the union representative claiming it totalled in excess of 38 hours a week.
Volunteer teachers at the school are paid stipends as little as $23,000 a year, have no employment entitlements such as leave, and do not receive superannuation, the inquiry was told.
Serious allegations of forced labour and servitude within the school could amount to modern slavery charges if it is proven on a larger scale, NSW anti-slavery chief James Cockayne said.
Redeemer pays for community phone plans and some devices are monitored, including reviewing call logs of phones belonging to members who have left the community, the inquiry was told.
Former school property manager and ex-church elder Glenn Frost, who joined the church at age three, accused the church of using government funding, school fees and donations to amass a $140 million property portfolio.
The portfolio features as many as 60 properties, including homes for staff and families, holiday homes and school camp facilities.
The school has been invited to give evidence in a second inquiry hearing on Friday.
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