The former drama teacher John Owen was a serial sex abuser and an education official's failures in investigating him could amount to a criminal act, according to a report.
Owen exploited the fear and awe he inspired in his pupils
That long-awaited report was published at midday on Thursday by the Children's Commissioner for Wales Peter Clarke.
Victims and parents say they are pleased with its scrutiny of years of child abuse by a prominent teacher in the Welsh language community.
But the man most heavily criticised, David Matthews - now the director of education for Bridgend - has rejected the criticism as "unjustified".
The Clywch inquiry was set up by Mr Clarke after Owen killed himself the day before he was due to stand trial on five courts of indecent assault against former pupils.
After leaving teaching, he became well known as the writer of a popular Welsh language youth drama called Pam Fi Duw (Why Me God?) - often described as Wales' equivalent of the school soap Grange Hill.
So far there have been no allegations of abuse during that period.
While teaching drama at Ysgol Gyfun Rhydfelen in Pontypridd, his big, bullying presence around the school was such that many pupils thought he was the head.
He exploited his charges' fear and awe of him to trick some of them into acting out sexually-explicit material in lessons and even in examinations for GCSE and A-levels.
With hindsight, the warning signs were there more than 20 years ago.
A catering assistant saw him with a half-naked boy on his lap. Owen managed to explain it away.
In 1986 an external examiner for the WJEC - the Welsh examinations board - stopped a performance in which a naked pupil simulated a sex act.
But she was told to go back and carry on by her managers at the examination board, for fear that the pupil's results might suffer if she did not.
She wrote a report but received no feedback from the WJEC.
Peter Clarke says children will be safer under his recommendations
In 1991, one mother was so horrified by the limited knowledge she had of her daughter's abuse at his hands that she wrote to complain. This prompted an investigation by the education authority.
Six pupils wrote statements - all complained of the excessive emphasis on sex during lessons.
One revealed that they had been told to feel each others bodies in the most intimate way during performances, and some said they had to simulate sexual acts.
A group of senior teachers also wrote to the education authority, saying Owen was unfit to teach because of his obsession with sex.
David Matthews, a district education officer for the former Mid Glamorgan education authority, was sent in to carry out an investigation.
What he heard should have warranted an immediate referral to police and social services.
But the commissioner says he is unable to identify any good reason why he didn't do so, and his failure could amount to a criminal act.
Mr Matthews - now director of education for Bridgend - is currently on sick leave, but has issued a statement saying he rejects the criticism as unjustified.
His then boss, Eddie Roberts, allowed Owen to resign.
Though some information was eventually passed to the police, officers did not have enough to warrant a prosecution.
The commissioner says the authority's failures amount to a cover-up.
Owen was even able to see some of the children's allegations against him. Some of his supporters -including some other staff members - then turned against the abused children.
Pupil was set against pupil, and the trauma of that experience has deeply marked some of the victims.
Many of Owen's victims broke down as they gave evidence
Owen then took a performance of Godspell around Wales, with a young cast, and directed a festival for the Urdd, the Welsh youth organisation.
Questions were asked about the allegations against him but because there had been no prosecution, he was allowed to continue.
He then wrote a book, Pam Fi Duw, about life at a south Wales valleys comprehensive school. It was turned into a successful TV soap, with Owen as the scriptwriter and later the director.
In 2001, four of his pupil victims, by now grown up, went to the police to say what really happened to them. Owen was charged with five serious sex offences.
He killed himself in a caravan at the resort of Porthcawl, in October 2001. He was on the run, having failed to appear in court.
The children's commissioner announced his investigation a month later.
When he took evidence, more victims came forward, and told Mr Clarke the full horror of Owen's abuse - which included rape.
Mr Clarke makes a series of 31 recommendations. They include:
A call for a national strategy to provide an independent counselling service for children and young people in education.
Sources of support to be identified and promoted in schools.
That serious disciplinary matters should be investigated by new tribunals, each with a legally qualified chair.
Education Minister Jane Davidson said the report was "deeply disturbing".
"The central issue that demands the assembly government's attention - and the attention of the whole assembly - concerns ensuring that the events at
Rhydfelen cannot be repeated anywhere else.
"We must have robust, dependable systems in place that protect children from harm and abuse, and ensure that responsible adults act properly upon what
children tell them."
She said it was essential schools and LEAs had clearer procedures in place, and that there had to be action from the WJEC to improve its procedures.
But Ms Davidson told BBC Radio Wales that the assembly - which debates the report's findings in September - would not be able to implement Mr Clarke's recommendations within the timescales he had stipulated, because of the amount of consultation required.
"It is very unlikely that we will be able to adhere to the deadlines," she warned.