Inmates of Wellingborough Prison were being left in their cells rather than being trained for future employment, according to prison inspectors.
Too many inmates are left in their cells for too long, says the report
In a report published on Tuesday, the Chief Inspector of Prisons, Anne Owers, said the institution was not fulfilling its role as a training prison.
Only half the prisoners were involved in work or education at any time, with the remainder locked in their cells for long periods.
Inspectors who visited the prison in August also found the race relations policy out of date.
They said there was no ethnic monitoring and no confidential complaints system.
Inmates felt safe
However, the jail was recognised for its good reception procedures and induction programme.
The inspectors also praised Wellingborough because 80% of inmates said they never felt unsafe and 75% said they were treated with respect by staff.
Ms Owers said: "Managers (of the prison) have two main tasks: to improve the quantity, quality and allocation of work and education and to put in place an active race relations policy."
Phil Wheatley, director general of the Prison Service welcomed the report.
"I am encouraged by the fact that opportunities for prisoners to engage in work or education have increased following the recruitment of three workshop instructors."
He also said that action was being taken to improve the prison's race relations policy.