Education, training and rehabilitation need to become the primary focus of jails, the chief inspector of prisons in England and Wales has said.
Charlie Taylor told the BBC that a "fundamental reorientation" of the prison system was the only way to reduce reoffending.
His intervention comes amid growing concern around overcrowding in jails.
The government says its new Prisoner Education Service will improve outcomes for those being released from custody.
But Mr Taylor suggested that jails were failing to reduce the risk of prisoners reoffending, and that many inmates were failing to learn to read.
Others, he said, were taking part in courses which would not help them get jobs in future.
He also argued that the high availability of drugs in some prisons was hindering rehabilitation efforts, as he called for immediate action to give prisoners the skills they need for life in the workplace.
Last week, the prison population of England and Wales - the area Mr Taylor is chief inspector for - was more than 87,000. Mr Taylor believes there is not enough space for prisoners to be provided with the activities they need for suitable rehabilitation.
