Transient children have hit record numbers in low-income schools as the housing crisis forces more renting families to move house repeatedly.
Numbers are still low, but the latest Ministry of Education data shows that 2.8 per cent of children in schools in the poorest tenth of areas moved at least twice last year - the highest low-income transience rate since records began in 2009.
In contrast, only 0.4 per cent of students in the richest tenth of areas moved at least twice, and that rate has been stable over the past eight years apart from a brief spike caused by the Christchurch earthquake in 2011.
NZ Council of Educational Research chief researcher Dr Cathy Wylie said the contrasting trends reflected growing insecurity for renters in the housing crisis.
"The shortage of rental and social housing has meant that families are often having to move out of where they were," she said.
"For example, if you are in social housing, you may find you have to shift out of the area where you were in one part of Auckland and now the housing is available in South Auckland.
"People at the higher end have more options available. They are usually going to shift within the same area. They have more control over their housing choices than poor people do."
Although on average only 0.5 per cent of children moved at least twice in any one year, the data shows that 15 per cent of all children who started school aged 5 in 2011 moved schools at least twice before they left year 6 at the end of 2016.
And continued transience had a dramatic effect on whether students achieved the National Certificate of Educational Achievement (NCEA).
Only 39.6 per cent of students who moved at least twice in their first three years of high school left school with NCEA Level 2, compared with 84.7 per cent of those who stayed in the same school for those three years.
"What people in low-decile schools say is that they have to work extra-hard with the kids coming in who are transient. They have to work quickly to make them feel part of the school and part of the family," Wylie said.
"In our last national survey, quite often when principals were talking about National Standards, they would say if they could separate out their transient students and those who are not transient, there is a difference."
One principal commented that children only just get accepted for a resource teacher of learning and behaviour, and then leave.
"They return many months later and the process starts again," the principal said.
Geographically the data shows extreme variation related to incomes, from a low of 0.2 per cent moving at least twice a year in the wealthy Auckland local board of Devonport-Takapuna up to a high of 5.1 per cent in the country's poorest district, Kawerau.
The next-highest rates of moving at least twice in a year were in Ruapehu (4.4 per cent), possibly because of movements in and out of the Waiouru army camp, Otorohanga (3.8 per cent), Wairoa (3.4 per cent) and South Waikato (3.3 per cent).
Within Auckland, the highest rates were on Great Barrier Island (3.6 per cent) and in Papakura (2.3 per cent) and Manurewa (2.2 per cent).
Ministry of Education deputy secretary Katrina Casey said overall national levels of transience had remained stable since 2009, apart from the post-earthquake blip.
"People move for all sorts of reasons, often to take up a new job," she said.
"Moving schools shouldn't be a barrier to learning as teachers are trained to assess a student's learning needs and tailor teaching to those needs.
"It may take some children a while to integrate into a new school especially if they have to move a number of times. But many children integrate well and are able to pick up where they left off at their former school."