That was an issue mainly in maths, science and technology. It was hard to attract staff in those areas because they could get more highly paid jobs in other industries.
Ms Brown said some schools reported many staff were near retirement age and they expected it to be hard to replace them.
John Paul College principal Patrick Walsh said the school had a number of teachers over 65, including one who was 72. Young teachers were coming through but he wasn't sure they were in the right subject areas.
There needed to be more scholarships and incentives for people to study things such as chemistry and physics, he said.
Often arts graduates were teaching those subjects.
"It's not their primary strength and that's a disadvantage for students who want to study engineering or medicine or architecture."
Reporoa College principal Steve Lewis said there was "no doubt" the teaching population nationally was ageing but his school had recently hired new staff.
"We haven't had too much trouble hiring and it has meant we have a good mix of young and more experienced teaching staff, but that being said, I am still wary of what is happening nationally."
Mr Lewis said the school had hired a new head of department for maths who was "showing great creativity and innovation within the subject.
"It can be hard hiring staff for subjects like maths, science and technology, but a lot of that comes down to how you market the school as a workplace."
The report stated principals had reservations about the impact of pending retirements on their schools.
Principals were, in general, less optimistic about retaining teachers and more pessimistic about recruiting.
There was a jump in teachers being used outside of their specialist area because specialists could not be found, says the report.
PPTA Secondary Staff Report
- 172 secondary and composite schools.
- Advertised jobs increasing and mean number of applicants per position declining.
- Proportion leaving for jobs outside teaching increased.
- Teachers leaving for "other reasons" such as retirement, accounted for the largest proportion of leavers.
- Maths, te reo, sciences and technology frequently mentioned as hard to staff subjects.
- Several references to the oversupply of physical education teachers.