A headmaster has been found guilty of breaching health and safety laws after the death of a three-year-old pupil.
Kian Williams, aged three, died in hospital after the fall
Kian Williams died in August, 2004, a month after jumping off steps at Hillgrove, a private school in Bangor, Gwynedd, while pretending to be Batman.
James Porter, 66, was convicted by an 11-to-one majority after a seven-day trial at Mold Crown Court.
The judge, who will fine the head later, said unsupervised access exposed Kian and other children to risk.
Kindergarten pupil Kian, from Bethesda, had been carrying a Spiderman toy when he jumped from the fourth step from the bottom of the flight.
He landed face forwards, causing head injuries which led to a coma and pneumonia, and died in hospital a month later.
The court was told the pneumonia that Kian had developed had been a strain of MRSA resistant to antibiotics, and there could be "no doubt" the infection had caused Kian's death.
The jury was told there had been only one teacher on duty supervising 59 pupils when the incident happened during the morning break.
The teacher had positioned herself so she could supervise both upper and lower playgrounds.
But she had been unable to monitor the steps - to which there was no physical barrier - from where she was.
James Porter had denied breaching health and safety laws
Summing up for the prosecution, Nicholas Jones said Kian had been allowed unsupervised access to the steps which exposed him and the 10 other three and four-year-olds in the kindergarten class to a risk to their health or safety.
He said more staff should have been on duty, and there was no reason why a gate erected following the accident in July 2004 could not have been put up before.
Defence barrister Patrick Harrington had previously told the court it was a "one-in-a-million" accident, and had highlighted the school's exceptionally good accident record.
Porter, who also owns the school, had told the court that Kian had known he was in an out-of-bounds area.
He said the playground supervision level was enough because of the ethos of the school and the pupils' self-disciplined behaviour.
Judge Rogers adjourned the case for sentencing, saying the penalty was a fine, but he would need up-to-date accounts before he could fix the level.
Porter, who had denied breaching health and safety laws, was given bail until the 28 September, when he will return to court to be sentenced.
His solicitor read a statement saying the outcome was a "major disappointment" for both him and his wife Sylvia, who had both run the school for more than 30 years.
It read: "This verdict means that a highly responsible and dedicated headmaster has been given a criminal record over a tragedy, described in court as one-in-a-million."
Kian Williams had been at Hillgrove School for two terms
Kian's parents, Jacqueline and Dafydd Williams, who are now taking legal action against the school, said they hoped the publicity surrounding the case would prompt other schools to check their supervision and possible hazards.
In a statement, Mrs Williams said: "My husband and I are in no way vindictive.
"Every parent knows you should put stair gates up to stop children climbing or falling down steps but there was no barrier to stop Kian falling.
"Schools and nurseries should be safe environments where parents feel totally safe leaving their children.
"We felt it was our duty to see that the circumstances of Kian's death were fully investigated for his sake and for the sake of children and parents everywhere."
Speaking on the steps of the court, Kian's grandfather Ken Williams expressed his relief at the verdict, saying: "Kian was not old enough to make decisions for himself. He was just a baby."