The government has conceded it is unlikely to meet its five-year target for reducing prisoner reoffending.
In 2012, the Corrections Department set a 25 percent reduction target by June next year, however its latest annual report showed the reduction rate was 6 percent.
However, it said the number of people who reoffended has fallen by 5000.
Veteran prison reform lobbyist Kim Workman told RNZ last week Corrections' target was "nonsense" and that "no country in the world" had reduced offending by 25 percent.
And the Salvation Army's director of social policy, Ian Hutson, said the failure was disappointing and the department needed to spend more on its rehabilitation programmes.
"It doesn't seem to take much to get a whole new prison built, whereas people seem slow to look at options of putting money at the front end.
"It's a whole lot better for the offenders, it's a whole lot better for the community."
However, Corrections said the lack of progress was due to factors outside its control such as "the rates of prosecution and conviction, the types of sentences imposed and court disposal times".
"Further, a falling number of new sentence starts with Corrections in recent years has brought about a change in the composition of the offender population under management.
"This now features a greater proportion of recidivistic offenders, more of whom have gang connections, and fewer first-time offenders."
Its figures showed the number of people who reoffended has fallen by more than 5000 over the past five years, while "the proportion of the offender population who are successfully engaged in rehabilitation programmes has never been as high as in the last three years".
Nevertheless, Mr Hutson said: "the results are clear proof that the approach to re-integrating and rehabilitating prisoners is just not working".
"The Corrections Department now acknowledges that many of the influences around re-offending by released prisoners are outside of its influence so this should be a reason to look for radically different approaches."
In June, the Minister for Corrections, Judith Collins, said close to one third of the prison population were in gangs and gang offenders re-offended at twice the rate of non-gang offenders.
She said tackling the gang problem would go some way towards reducing re-offending.
RNZ reported last week the number of inmates has hit a new peak of almost 10,000. This is 500 more than the Ministry of Justice's forecast.