Canterbury Prison has been severely criticised for struggling to achieve its objectives.
Inmates spend "most of the day" locked in their prison cells
In a report released on Friday, the Chief Inspector of Prisons said 40% of the 280 inmates at the training and resettlement jail had nothing to do.
It said they spent at least 19 hours a day locked in cells which are old, in poor condition and overcrowded.
But the report also stated that the prison was a safe environment with very little bullying or self harm.
The 203-year-old jail was given a new function two years ago to give men sentenced to less than four years the education or skills they will need when they get out.
Lance Kennedy, head of resettlement at the Category C prison, agreed the report, from Chief Inspector of Prisons Anne Owers, had pointed out shortcomings.
"When a prison changes from one role to another obviously it's going to take some time before we can get everything into place.
"In terms of purposeful activity, an awful lot of investment is coming into this prison in terms of extensive rebuild, which will hopefully give us more purposeful activity places.
"In terms of resettlement, we need to do a little bit more in finding housing and jobs for people before they are released... so that they have got somewhere to go, which reduces re-offending," he said.
Governor of the prison, Helen Renaldi, said she was pleased to see a recognition that it was a safe place where prisoners were "treated decently".
She added that the report gave the prison "a benchmark from which we can progress".