The Post Primary Teachers Association says figures obtained under the Official Information Act show new truancy services are missing their targets for getting children back to school.
It says in first quarter of this year, only 37% of truancy cases were resolved within ten days, compared with an Education Ministry target of 90%.
The ministry this year combined two different types of truancy service, reduced the number of organisations providing the services and increased spending from nearly $6 million a year to $9 million.
Principals Federation president Philip Harding says the Education Ministry needs to fix problems with the new service as it is not working as well as it used to and needs to change.
"You rely on truancy services to go out, into the streets, into the homes and to find these children and to find their parents and have those difficult conversations," Mr Harding says.
"It is very time-consuming work if you can't get hold of someone to follow up on a child who is missing right now."
Mr Harding says he welcomes the the ministry's plan to review the new service.
Post Primary Teachers Association president Angela Roberts told Nine to Noon the shift to the new system has gone badly.
She says the contracts were not signed until January, the computer system was not ready to go live and the key performance indicators the providers must report against are difficult.
"So the whole thing's a mess, the providers are actually nobbled in the process," she says.
Ms Roberts says many of the new services are finding a much higher level of difficult truancy than the ministry told them to expect.
Porirua College principal Suzanne Jungersen says changes have left her school worse off.
She told Nine to Noon the service in her area now has fewer staff working on truancy and does not deal with difficult cases.
The Ministry of Education says the new service is still bedding in and it will review the system at the end of the year.