A charity is accusing Corrections of making it too difficult for people to volunteer in prisons, with some waiting months to receive official approval.
Charity organisation Howard League for Penal Reform said it provided 100 volunteers to prisons throughout the country - but could deploy triple that if allowed.
Volunteers for the charity visited the prisons once a week, to teach inmates Te reo Māori, the road code and bee keeping.
But its most important role, according to Howard League chief executive Mike Williams, is offering a one-on-one tutoring service to near-illiterate prisoners.
A service that some prisoners would struggle without, Mr Williams told Nine to Noon
"Most of these prisoners, they have a little bit of reading so you're building on something. I think only twice have we actually had to teach the alphabet," he said.
Mr Williams acknowledged that Corrections did provide some literacy lessons to prisoners, but said those were in a classroom situation where the most illiterate would almost surely fail.
He said that if the prisoners could not grasp basic literacy, any hope of future employment would likely be dashed because about 84 percent of entry-level jobs require a driver's license - which can only be attained by passing a written test.
"It's also your method of identity ... you can't get a bank account without a driver's license" he said.
Jenny Clark used to volunteer for the Howard League at the Rimutaka and Arohata prisons in Wellington.
She said she would often spend 45 minutes travelling to the prison for a pre-booked literacy class, only to be told the lesson was cancelled.
"Sometimes the prisoners were actually scheduled for two things at once, although I'd booked a week in advance," Ms Clark said.
"And perhaps the other thing may have been like a sudden doctors visit or something, but I wasn't told ... nobody phoned me to say 'ah your prisoner is not actually going to be available'."
She said the prisons needed to have more rooms and a better scheduling system, so volunteering could be easier for the volunteers and Corrections staff.
"I know there are an awful lot of people who are willing to volunteer and that's a huge economic resource for Corrections, but they are not able to use them because they haven't got rooms, they haven't got times, so they can't allocate 50 volunteers to 50 prisoners."
Corrections' Offender Employment and Reintegration director Stephen Cunningham said there were only seven staff members throughout the country who were dedicated to co-ordinating volunteer efforts.
And for the South Island, that role was vacant.
Mr Cunningham said the volunteer application process was rigourous and took a great deal of manpower to complete.
"We need to make sure that the volunteer has gone through the justice process, they obviously need to be trained in a number of ways, we need to ensure there's no unintended conflict of interest and we need to ensure that they are safe," he said.
Mr Cunningham said staffing levels throughout Corrections were on the rise and that the department appreciated all the work volunteers did within prisons.