An international school in London has been told to do more to safeguard its pupils after a convicted paedophile drugged and abused boys in its care.
More than 54 pupils at Southbank International School were abused by William Vahey between 2009 and 2013.
The serious case review said its safeguarding policies had failed and teachers did not report their concerns.
The school's board said it continued to provide support to those affected and was addressing the recommendations.
Vahey, 64, who had a child sex offence conviction in California in 1969, killed himself two days after the FBI filed a warrant to search a computer drive belonging to him.
Indecent images of boys aged 12 to 14 were found on a USB stick.
The Local Safeguarding Children Board (LSCB) report found there had been opportunities to recognise the risks posed by Vahey at the school "but due to a combination of factors these were not grasped".
Reasons included a lack of leadership, staff not knowing how to recognise the signs of a sex offender and a reluctance to report a concern without "firm evidence".
The report said Vahey quickly established himself as an "informal" teacher who normalised behaviour, including having pupils in his room on residential trips, watching boys shower and making jokes with sexual connotations, enabling him to be "hiding in plain sight".
The report said staff and pupils fell ill on a number of his trips, which was often described as "dehydration, but now believed to be due to the administration of drugs by Vahey".
Three incidents were reported but adequate investigations were not held.
David Smellie, chairman of the school's board said: "We will review the report in every detail to ensure any necessary further actions are implemented.
"The safeguarding of children is an ever-present priority and we will always look at opportunities to further strengthen our practices."
It said following its own independent review it had brought in mandatory criminal record checks, an independently chaired safeguarding committee and greater reporting obligations for all staff to follow.
The LSCB report concluded the school had dailed to meet standards in safeguarding, communication and quality of leadership but had made "good progress" with school trips.