A prison, previously labelled as "challenging", has no action plan to tackle violence and self harm, inspectors have found.
Violence had increased "considerably" at Swaleside in Kent since inmates took over part of a wing in 2016, the HMP Inspectorate of Prisons said last year.
Returning in September they found "not enough had been done to meet the concerns of the 2018 inspection".
The inspectors said the number of violent incidents remained high.
"Despite this, managers had not thought hard enough about what was driving violence at the establishment," they reported.
"There was no meaningful strategy or action plan to reduce levels of violence.
"Likewise, there had been no reduction in the number of self-harm incidents, yet managers had not developed a strategy or action plan to address this problem."
They did find a reduction in the use of illicit drugs in the the Isle of Sheppey jail.
The inspectors said the prison had acted to support inexperienced staff, but they had "yet to translate into a confident and authoritative staff group".
"We saw many examples of antisocial behaviour going unchallenged by staff."
Peter Clarke, HM Chief Inspector of Prisons, said: "This was a disappointing review, and too little progress had been made in the nine months since the  inspection.
"Managers had, in our view, failed to act with sufficient diligence and rigour concerning the key recommendations we made in 2018."
Swaleside, opened in 1988 and houses more than 1,100 inmates, many of whom have psychological problems.
Among its population are an entire wing of vulnerable prisoners, another for sex offenders and a number of lifers.
"We found a single offender supervisor managing 170 prisoners convicted of sexual offences, which was simply unworkable," Mr Clarke said.
A Prison Service spokesman said: "This review recognises that HMP Swaleside has improved since its last inspection, particularly in tackling the drugs responsible for much of the violence in prisons.
"Since this inspection took place, additional training has been given to staff to help reduce levels of self-harm and we have put in place more activities to help prepare prisoners for their release."