Children are falling behind other students in their schoolwork as rising rents and a housing crisis force record numbers of low-income families to change schools.
New data shows that almost 36,000 children changed schools last year, including 3400 who moved at least twice in the same year.
The official transience rate, counting only those moving at least twice in the year, has been steady at around 0.5 per cent in each of the past eight years, but the transience rate in schools serving the poorest tenth of the population rose to 2.8 per cent - the highest since at least 2009
Education experts say while affordable housing is often to blame, job losses and family violence could also cause transience to rise.
At Leabank School, a decile 1 school in Manurewa where most parents are renters, 49.1 per cent of students moved at least once during the year, and that was after excluding new entrants who started at age 5 and seniors who left to go to intermediate.
Principal Rex Maddren, who has led the school for 17 years, said the figure sometimes dipped into the 30s and had never been above 50 per cent. He said the two main drivers were housing and family violence.
"It depends on how many people don't have a house and are living with relatives or in garages," he said.
"I think higher rents would definitely be a factor. A lot of people are moving because they can't afford the rent. We feed a lot of the kids - they can afford maybe the rent but not then to feed the kids.
"A lot of the cases in our families are related to family violence or family issues where they [children] have been removed or taken away and come back. I think when people are in distress they don't behave necessarily as calmly as you would expect."
He said moving homes usually meant children missed some days at school, and their learning suffered.
Barbara Ala'alatoa, principal at decile-2 Sylvia Park School, has shown that the new students who joined her school last year - 20 to 25 per cent of her roll - fell behind other students on national standards.
For example, 77 per cent of stable students who stayed in her school all year achieved national standards in reading, but the average for the whole school dropped to 72 per cent after including the transient students.
In maths, 74 per cent of the stable students achieved the standards, but that fell to 70 per cent after including the transients.
"We use that data to show parents that those kids that start and finish with us do really well, nearly in every case without exception," she said.
The new data, provided by Education Minister Nikki Kaye in reply to a written question from Green MP Catherine Delahunty, shows that the highest rates of students changing schools at least once last year were in Northland (10.8 per cent), the West Coast (10 per cent), Gisborne (9.4 per cent) and the Waikato (9 per cent).
The lowest rates were in the urban areas of Canterbury (5 per cent), Auckland (4.8 per cent) and Wellington (4.3 per cent).
Tai Tokerau Principals Association president Pat Newman said this was partly because losing your house or job in the city did not necessarily force your children to change schools.
"If you're in Auckland you can shift house without having to change schools, but if you're in a small rural town and you have to shift house you generally have to shift town," he said.
But the same housing issues were driving higher transience in Northland, he said.
"Since Auckland has priced itself out of the market, a lot of Aucklanders have bought houses up in Whangarei to rent out and the rents have gone up $100 or $150 a week," he said.
West Coast Primary Principals president Bevan Clark said many Coast families had been forced to move after the closure of mines and other industries, such as the former Holcim cement works at Westport.
Delahunty, who lives in Thames, said Aucklanders fleeing to the Hauraki and Coromandel districts were also driving up rents there.
Rental bond data shows that average rents in the year to July rose by 6.4 per cent nationally and by 9.1 per cent in Northland and 8.2 per cent in the Waikato, as Aucklanders also moved into that region. Rents in Auckland rose by 3.5 per cent.
The average wage rose by only 2.2 per cent.
Over the past five years rents rose by 26.2 per cent nationally, with the biggest jumps 32.7 per cent in the Bay of Plenty, 27 per cent in Northland and 25.7 per cent in the Waikato. Auckland rents rose by 24.5 per cent.
The average wage rose in those five years by 13 per cent.