Jailed former Heart of the City boss Alex Swney is teaching fellow inmates how to read and write.
Swney, 59, was jailed for five years and seven months in June 2015, after being found guilty of tax evasion and "sophisticated" offending spanning more than a decade.
The crimes involved more than $4 million.
It is understood he will be eligible for parole in May.
New Zealand Howard League for Penal Reform chief executive Mike Williams, a former Labour Party president, yesterday told the Herald on Sunday of Swney's work with fellow inmates via one of the organisation's peer-to-peer literacy programmes.