The dean of Canterbury University's law school says a relentless bias is to blame for the under-representation of women on boards.
Information filed by NZX-listed companies show, on average last year, 17 percent of directors were women.
The ratio is the same as 2015.
For the final quarter of 2016, the percentage fell to 13 percent.
Although the information derives from only 125 listed companies, Professor Ursula Cheer said the real percentage could be lower. Many would want to hide the lack of balance, she said.
Ms Cheer is the first female dean of Canterbury University's law school and the only one in New Zealand's six law schools.
She said the problem was complex.
"I think it's a combination of women not being appointed - and that's just a relentless bias that's both acknowledged and isn't - but it's also a case of some women still not putting themselves forward and that can come down to confidence."
Ms Cheer favoured quotas as they made having women on boards normal.
The chief executive of Governance New Zealand and Women on Boards, Linda Noble, agreed quotas worked overseas.
"It's almost like a dirty word here when you talk about quotas because I don't think any woman wants to be on a board just because she is a woman," she said.
"But it does make a real difference."
Ms Cheer said students studying law were two-thirds women to one-third men.
"That could have a big impact on the profession... which doesn't appear to be prepared or doing much about this," she said.
"If you look at the structure of a lot of law firms you see mostly men at the top and then mostly female associates."
A Women in Law Society was recently established at Canterbury University. At its inception it had more than 100 members, including Ms Cheer.