A controversial youth prison has been rated as inadequate by watchdogs as it emerged inmates were able to access pornography.
Ofsted delivered a critical assessment of Medway Secure Training Centre in Rochester, Kent, saying the stability of the facility "has been sorely undermined by a combination of significant factors".
Police launched an investigation earlier this year following a BBC Panorama programme which went behind the scenes at the unit.
The Government announced it would take over the running of the facility, which was previously run by G4S, from July.
Ofsted carried out an inspection of Medway in June, before the change.
Its report said the centre had lost significant numbers of staff at junior and senior managerial levels, adding that most staff were very inexperienced.
Levels of violence in the centre were said to be very high and growing.
"This includes violence between young people and violence towards staff, despite a small and stable population of young people," the report said.
In the six months prior to the inspection, the centre reported 31 assaults on young people by other young people and 13 fights. Over the same period there were 51 reported assaults against staff.
Security arrangements were a significant concern, inspectors found.
In recent weeks, two USB data sticks containing highly inappropriate material have been found in areas accessed by young people, the report said.
It added: "It is clear that young people have been able to access pornography although it is not clear how many young people have been involved."
In another case insufficiently secure storage of a broken pool cue and inadequate searching resulted in a young person being able to remove the item from a sterile area undetected, taking it from the living unit to the gym, and attempting to assault another young person with it, according to the report.
As well as overall effectiveness, Medway was given an inadequate rating for four categories - the safety of young people, promoting positive behaviour, the care of young people and the effectiveness of leaders and managers.
There were "good" ratings for the resettlement and health of young people, while the achievement of young people was found to require improvement.
Some services within the centre have managed to continue to provide good quality interventions, the report said.
In February, G4S said it was selling its UK children's services business, which includes 13 children's homes and two secure training centres - Medway and Oakhill in Milton Keynes.
Jerry Petherick, managing director for G4S custodial and detention services, said it was a "deeply disappointing" report following a number of years in which Ofsted rated Medway as good or outstanding.
He said staff turnover was a real problem, adding: "This was clearly a period of intense disruption which created uncertainty and instability for the young people and staff at the centre and it proved extremely challenging to maintain appropriate staffing levels and standards."
Lessons learned at Medway will be applied through a far-reaching review of standards, skills and processes at Oakhill, Mr Petherick said.
He added: "I fully expect this to translate into substantial changes to the way in which the centre is run."
Lord McNally, chairman of the Youth Justice Board for England and Wales, described Ofsted's findings as "completely unacceptable".
:: Twelve people have been arrested in connection with the police investigation into Medway STC. Rebecca Harold, 24, of Maidstone, has been charged with common assault and will appear at Medway Magistrates' Court on August 23. Nine other individuals are on bail until next month, while two people have been released without charge.