Many of Owen's victims, now in their late 20s and 30s, wept as they told the Children's Commissioner how he had abused them at Ysgol Gyfun Rhydfelen.
John Owen taught at Ysgol Gyfun Rhydfelen
They told an horrific story of the way he tricked them into believing the sexual acts they carried out or pretended to carry out weren't abuse.
Giving evidence at the inquiry, one former pupil - abused during special drama lessons - had a stark warning.
"If there is somebody out there abusing children or young people sexually or whatever,
one day these children and young people will grow up and one day there's going to be a knock on the door and that's what happened to him."
It was 20 years before he was able to talk about his
experience with Owen.
Another told BBC Wales' Tarw Naw Welsh language current affairs programme: "The man that I am now desperately wants to save the child I was then.
"But that child has gone so if I can help anyone else then that's got to be good. Because being a teenager is such a difficult thing anyway. Such a traumatic time in your life to be preyed on by someone like this is dreadful."
One parent told of the moment their child first told them about the abuse they had suffered years before.
"Our child came home and asked to speak to us in this very room and said that this abuse had taken place over a number of years," they recalled.
"And we were absolutely horrified, shocked, totally shocked. It was so difficult to handle
I think we cried for hours maybe days from time to time
and the thoughts of what our child had endured over the years was too horrible to contemplate at times. But at least now we were in a position to offer support."
Another former pupil said that when she realised what had actually happened to her it was like a car hitting the wall.
Below is excerpts from others told the children's commissioner in their testimonies:
"John Owen took drama and twisted it and played out his sexual fantasies with it, and he preyed on the innocence of children who wanted to do drama, and he turned it into something we couldn't understand at all.
"And whether it be dancing naked in a classroom or being severely sexually abused in his bedroom or in private wherever that took place I don't differentiate between the two things. I think they're both the same.
"I knew there was no escape for me at that time, that I couldn't turn around and tell him that he was wrong because I feared him physically and I feared him emotionally."
"I want people to know that for me, the abuse wasn't just the physical thing. It was the fact that he'd tricked me into having no idea that it was abuse."
"Part of me would like nothing more than to face him now across a court room and ask him to deny what he did to me. Unfortunately I won't get that opportunity."