Some Northland 6-year-olds have attended up to eight schools because of their families' constant moving.
Te Tai Tokerau Principals Association is so concerned it is collecting data about transient students from 80 schools to determine the extent of the issue.
Leanne Otene of Manaia View School said students who hop between schools were the biggest problem facing schools in the region.
"I've got some kids now that are 6-years-old and have been to eight schools already," Ms Otene said. She estimated that if her school had 200 students at the start of the year, by the end of the year 80 would be replaced by new students.
It was very rare that students were moving to another school but rather moving out of the area, Ms Otene said. Most of the new students coming into the school are below, or well below, the expected learning level.
"If they are here for a month, every day counts," Ms Otene said. "For me, there is a sense of urgency when you enrol a child because you don't know how long they are here for.
"Families of transient students likely do not have a choice about moving because of socio-economics," she said.
Families moved to find employment or stable housing.
Moving made it difficult for children as they need stability, Ms Otene said.
"The most important person to a child, aside from their whanau, is their teacher."
All Northland schools faced the issue, not just lower deciles, she said.
It put pressure on teachers because often national standards data suffered when children came into the school behind.
Te Tai Tokerau Principals Association president Pat Newman said the reasons for the high number of transient students in Northland were "numerous" but could largely be attributed to socio-economics.
It was not unusual to have students that have gone to eight or nine schools, Mr Newman said. "Five schools you wouldn't even raise your eyebrows at".
The association was collecting data about transient students and the high levels of negative behaviour in Northland schools. Mr Newman expected the results to be released early next year. New Zealand Principal Federation president Phil Harding said he knew Northland schools were struggling with transient students. "I'm certainly getting the sense from Northland principals that the issue is huge," Mr Harding said. That put extra pressure on teachers to give those students extra help, despite the fact they may leave again soon, he said.