The WA Catholic Education Commission has been fined $9000 after a six-year-old child wandered away from a Bayswater after-school care unnoticed and was found by a member of the public 20 minutes later.
The girl left St Columba's Primary School around 5pm on February 2 - the second day of the school year.
The tribunal, earlier this month, found the child slipped away unnoticed through a gate that had a self-locking mechanism which failed to operate.
"Her absence was only noticed when an unknown member of the public found her at the Bayswater Family Centre some 250 metres from the service and called her mother, who then advised the service at approximately 5:19pm," the tribunal found.
"Her mother returned her to the service at approximately 5:27pm.
"Since the incident, CECWATA has installed a new swipe card mechanism on the gate to further secure its operation."
The school is the tenth service to go before the State Administrative Tribunal for losing a child since two children were lured from a North Perth child care centre and sexually assaulted by a 52-year-old man in April 2016.
The service was fined more than $40,000 over the incident in September 2016.
One Tree Children Services in Wickham was fined $10,500 in November after a one-year-old left the service through a gate on June 27 2016, and was later found on a busy street by a parent.
"The parent had to park her car and run after the child, picking him up when he had walked approximately one metre onto Carse Street," the tribunal found.
"Educators at the service were unaware that the child had been missing, and that the gate was open."
Another Catholic school, Sacred Heart Primary School, is also in mediation with the tribunal after a child left the Thornlie school unattended while two Camp Australia after-school care centres at Coogee Primary School and Jandakot Primary School are in mediation for two five-year-olds escaping from their care in 2016.
The man convicted of sexually assaulting the two North Perth child care centre children, a five-year-old boy and four-year-old girl, will be sentenced in October.