Ōtāhuhu College principal Neil Watson said he noticed a big increase in students leaving school before the year was over especially among Year 13s.
"We've probably lost 30 Year 13s this year who have left early and normally we'd expect to lose maybe five to 10 so probably an extra 20 students have left early and although all of them have gone to jobs.
"We are concerned about their future career prospects without gaining University Entrance, without gaining level three."
He said some were leaving because they needed to support their families, but many were giving up on school because they were so far behind in their learning.
"They're coming back to school, school's operating as normal and they've realised that they've fallen significantly behind where they need to be and it becomes a struggle and despite efforts by schools and by teachers and the support staff to keep them in school, they're dropping out."
Last year, nearly one-in-five school leavers was under the age of 17, the highest figure in a decade and a third of all leavers had no qualification or only level one of the NCEA.
Papatoetoe High School principal Vaughan Couillault said more teens had weekend work and more had found fulltime work and left school earlier than normal.
As a result, the school had fewer senior role models for its younger students and there had been a range of other effects.
"A lot of our students have got part-time jobs and want to work on a Saturday and so our Saturday sports teams haven't been able to function so that's a bit of a new thing for us. Kapa haka, for example, all our senior boys have left and gone and got employment and so we find difficulty at pōwhiri time getting the male voice side of what we need to do."
He said some teens were waiting to finish their NCEA qualification before leaving, but others were not.
"Some I think will jump into employment at the end of this term because they might have got enough to get them over the qualification mark. Others, the lure of that money, be that 45-grand or 55-grand a year, is a little bit too much and they're willing to sacrifice finishing off the qualification for that short-term gratification of getting the payroll started," he said.
Couillault said some but not all of the students were leaving because they needed to support their families.
Employers appeared to be hiring teens for jobs that used to be filled by working holiday makers, he said.
James Cook High School principal Grant McMillan said many students were taking jobs so they could support their family.
"A number of young people have basically come in and talked to us and said 'look I've got a job, family income's really tight right now, the rent's gone up, I now have to go out and work to help our family pay our bills and things, I hope to come back one day'. The reality is they're unlikely to."
McMillan said his school usually lost just a handful of senior students early, but this year the numbers were much higher.
"This year we have 20 per cent of our Year 13 students, that's one-in-five leave during the year before their qualifications are completed to go into employment. At Year 12 we would also have a smaller number as well, but ignoring those that we've actually helped into apprenticeships and that sort of thing we've had about a fifth of them leave as well."
McMillan said the school tried to accommodate students so they could stay in school and work. For example, allowing students who worked in the evenings to start their school day later.