The Education Ministry has been trying to find schools for more than 100 children who have been kicked out of other schools.
At the start of May it was working with 134 students under the age of 16 who had been excluded from a school.
It said 96 had been out of class for up to 40 school days, but 11 had missed more than 100 days.
The figures come amid ongoing complaints from the Principals' Federation that schools do not get enough support when they enrol pupils with a history of violent or disruptive behaviour.
The ministry said schools had 10 days to find a new school for any students they excluded and if they failed to do that, the ministry took over.
It said re-enrolling excluded young people was sometimes complicated.
"Students may have situations that are destabilising through a range of social factors and complex whānau circumstances. Factors can include the family being transient and address is unknown, family and/or student not engaging with the process or Youth Justice or Oranga Tamariki involvement," it said.
"It is our responsibility to work with the family and education providers to find an option that means the student can engage and participate in education.
"We will coordinate with other agencies to locate students, or if an address is known, our education advisors will often work with support services to establish contact and arrange a home visit.
"We can direct an enrolment and make sure the right supports are in place to transition the student back into learning, or if there is no local school option we can build a plan with whānau for the student to continue with their education through Te Kura."
The ministry did not provide the longest wait times for the students it was working with, but a parent told RNZ her child was out of school for 18 months following an exclusion.
She said the long wait was partly due to the Education Ministry recommending schools that did not suit the family, and when a school was agreed on, the child had to wait six months before they were old enough to start classes.
"We honestly did not expect it to take that long. We didn't necessarily expect it to be a fast process because of our child's complex history around education but we certainly wouldn't have expected it to take 18 months," she said.
"Our child kind of ended up bored because they spent all that time at home. From a parental point of view it was stressful."
Another parent told RNZ her son was out of school for five months following an exclusion last year and now he worried that any long break from school would result in him moving to a new school.
"It still to this day has a huge impact. Every time there's a school holiday he keeps thinking that he's going to have to go back to a school that was not treating him right," she said.
"The Christmas holidays are even worse because he's off for longer so he reverts back to not being in school. If they had been able to get him back into another school sooner it wouldn't have been so traumatic for him."
Both women told RNZ they believed more could have been done to get their children back to school faster.
Exclusion applies only to children under the age of 16 - older students can legally leave school - and the school that does the excluding has to try to find another school.
Secondary Principals' Association president Vaughan Couillault said finding another school was not a quick process.
"Often the families need a couple of days to decompress and that five days really quickly turns into 10 days even though we're going as fast as we can," he said.
"Then you start engaging with schools, be that by telephone or by fax, setting up times for families to meet and have time off work or whatever it might be. Things can get out to 20 or 30 days even though everyone's working pretty hard to get people re-engaged."
Principals Federation president Perry Rush said the ministry would find it easier to re-enrol children if it provided more support.
"We know these young people are highly complex and many are struggling and dis-regulated in their learning.
"So schools will be looking for the appropriate support to assist them to help the young person but also to ensure there's not going to be continuing disruption in the new school setting."
Challenges getting kids back into school
Berhampore Primary School principal Mark Potter told Morning Report it could be "extremely tricky" for some children to get back into class.
"Especially if the schools aren't prepared or the appropriate agencies aren't in there supporting the child with their complex needs.
"I think there's a lot of things at play here. When a child is in a situation of needing to re-enter school, quite often schools get a little bit gun shy by that stage because they are under a lot of pressure from their communities about who those communities would like to see in their schools. That's unfortunate, that can actually create barriers."
One of the biggest issues, in Potter's eyes, was that not enough schools were not prepared to meet the needs of such complex situations."
"It's very difficult for schools to access services they need. Either there's just not enough capacity within the agencies or the Ministry of Education ... you are talking about lengthy wait times ... we know from experience it can take months to get the right agencies to support you with a child."
Some principals did experience pressure regarding the children they allowed in.
"Some parents resent that there are children that require quite a lot of effort and support and the funding systems and the resourcing formulas are not geared to gear up to meet the needs of that child, so it can become pressure on a principal to say 'we don't think that child should be in a class with our child'. And that'd be extremely challenging for a principal."