An Auditor General's annual report of schools accounts has revealed seven schools have required letters from the Education Ministry pledging financial support.
The report also highlighted instructions for using $12,000 grants for principals' well-being were "unclear" and some schools spent the money on personal trips and gym equipment which was "not appropriate".
"Some schools spent the funding in ways that could be considered to confer a private benefit, which is generally not appropriate for public funds," it said.
Kate Gainsford from the Secondary Principals' Council told Breakfast schools are under "immense financial pressure" and she was surprised only seven required help from the Education Ministry.
"I'm surprised, because there's a pretty extraordinary list of [financial] pressures on the schools at the moment," she said.
Gainsford said schools are dealing with everyday cost-of-living pressures that ordinary households face, as well as "unexpected and unbudgeted" costs like bringing over new teachers from overseas.
"If I need to employ a teacher from overseas, that's another $10,000 worth of unbudgeted costs that I need to pay recruitment agencies," she said, "and if I need to bring over three teachers it's $30,000. That's a lot of money."
She said New Zealand's system differs to other countries as a lot of the financial risks of running schools and the "big, multi-million-dollar projects" are shouldered at local board and local principal level, which she said brings 'big risks".
She said a large part of the problem is that principals and school boards aren't equipped with financial knowledge when they enter the role.
"Boards are genuinely motivated to do good in their communities [but] it's not required that they have financial expertise and even in the preparation for principals, it has been pointed out that there's no financial training," Gainsford said.
She describes new principals as "under-prepared" to handle the financial pressures of running multi-million-dollar projects that schools are required to carry out.

Gainsford said the Auditor does a great job of pointing out the flaws in the school's accounts, such as "basic things" that should not happen.
"Principals should never be signing off on their own expenses, that's pretty basic," she said.
"So, when it comes to finely-grained advice from the Auditor-general it makes boards and principals aware of the expenses.
"There is a $6000 allowance that's been signed into the collective agreements, but the intention for that is to address the retention of principals," she said.
She said a lot of principals are leaving, not to go into promotion or other parts of the profession, but simply leaving the profession.
One of the seven schools in financial trouble is New Zealand's oldest state secondary school, Nelson College.
Nelson College board of trustees presiding member Richard Smith said in a statement to 1News the college has been "transparent" about financial difficulties and is working on a plan to address the debt.
"Like many institutions, Nelson College faces financial pressures, and we are navigating these challenges with the support of the ministry and our community," Smith said.
He said it was important to clarify the financial hardship "does not imply any wrongdoing on our part" and that the school remains dedicated to fiscal responsibility, student welfare and being a provider of quality education.
"We are committed to working towards a stable financial future."
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