Studying a wide range of educational courses in jail makes prisoners in England and Wales significantly less likely to reoffend, research suggests.
A sample of 3,000 prisoners with access to study showed 19% had reoffended within a year of release, compared with 26% of 3,000 similar inmates without.
The study is part of a wider look at the effectiveness of a variety of initiatives to reduce reoffending.
Participation in distance learning was found to be the best reduction method.
The research was carried out for the Ministry of Justice, which is looking at the effectiveness of a number of voluntary and community sector schemes for reducing reoffending rates.
The sample group included people studying a range of courses from Open University degrees to vocational qualifications, funded by the Prisoners' Education Trust.
The PET's chief executive, Rod Clark, said education courses were cost-effective.
"Courses we fund typically cost £250 a piece", he said, "which is a minor cost when set against the £37,648 annual cost of a prison place."
Giving prisoners educational opportunities was vital, he said, "if we want to stop people falling back into a life of crime when they leave".