Boys should be allowed to have long hair at school - Victoria Uni law professor Dr Dean Knight

New Zealand schools shouldn't force boys to cut their hair, says a legal expert.

The recent case of James Hunt, a 13-year-old who last week had to cut his long hair in order to attend Auckland Boys' Grammar, has brought the issue to public attention.

It's far from the only school that doesn't allow male students to have long hair - Westlake Boys and Wanganui Collegiate School forbid hair that touches the collar, while Palmerston North Boys' High School and Otago Boys' High School say hair must be "neither long nor too short".

Dr Dean Knight, Associate Professor of Law at Victoria University, has followed the shifting nature of school regulations for much of his legal career.

"They're a vivid expression of law, power and authority," he told Newshub.

"It's tricky stuff. The mood ebbs and flows on law, and these are deep questions."

He uses case like that of Lucan Battison (who took St John's College to court over his long hair in 2014 and won) when talking to high schoolers about studying law because they're a useful microcosm of where society is at in relation to certain social issues.

The High Court ruled that St John's College's decision to suspend Lucan was unlawful and that the wording of its hair rule was vague. It did not make a judgment on whether it was unlawful for the school - or any other school - to force its students to have short hair.

Dr Knight says he has "real concerns" over schools that enforce hair regulation rules with the threat of expulsion.

"I suspect the courts would dislike it," he says in regards to James' situation. "I certainly find it problematic."

The fact that James was in zone for Auckland Boys' Grammar - a public school - is a key detail, he says. It's also of note that the school gave him no other options, such as being able to tie his hair up.

Such rules are "ripe for being challenged" in court, he says.

"What educational purpose do these rules serve? Conformity is not a blank cheque for discipline."

He says while courts generally give schools a "degree of latitude" over how they enforce their rules, they can intervene if punishment is deemed "ugly or flawed" or disproportionate to the supposed rule-breaking.

"My underlying concern is that these rules have a reach outside of school. Unlike a uniform which can be taken off, the student has to have short hair on weeknights and weekend too. It reaches right into personal autonomy."

Auckland Boys' Grammar headmaster Tim O'Connor told Newshub the school would not publicly discuss cases involving individual students.

"We are focusing our attention on starting the 2019 year in a positive fashion with all 2600 young men," he says.

"Our rules are regularly assessed, reviewed and discussed with our School community, who support our approach."

Dr Knight says schools tend to have "weak excuses" about safety in the schoolyard, but don't seem to have the same concern for long-haired girls.

"It's unjustified gender discrimination. In 2019 you've got to have question marks about it. Society is moving quickly, schools risk staying in the dark ages."

Schools could also run into religious or cultural discrimination if no provisions are made for male students who have long hair. Sikh men traditionally don't cut their hair, and long hair on men is common in several Polynesian cultures.

"The law would be seriously concerned about that," says Dr Knight. "Schools need to be careful."

He says if students like James were to pursue legal action that reached New Zealand's highest courts, those courts could potentially rule that those laws are unlawful or unjustified, although it would depend on the context and how such rules are framed or enforced.

The Ministry of Education could also provide guidance to schools on hair regulations, such as when it updated its sexuality education guide in 2015 to say schools may consider offering gender-neutral uniform options to avoid reinforcing gender norms.

Dr Knight says the issue is more to do with personal autonomy than freedom of expression, which is "never absolute" under New Zealand law.

"I struggle to see any justifiable reason for boys not having long hair of young women have long hair," he says.

"Short hair on boys seems to be seen as having inherent value or tradition. Either it's tradition from a day gone by, or it's conformity. It doesn't hold up, it doesn't have a strong rationale. These cases expose the weakness of the rule."

So why do so many schools still enforce hair length regulations?

"Power and authority," says Dr Knight. "There is a sense that schools are microsocieties, and some of the people running them have very conservative, traditional views.

"[There's an] argument that students and their families choose to buy into these rules, but we all have the right to education under the Education Act. When it's people in zone for their local school, the choice argument falls away."

He says school rules and education-related laws have changed significantly since he was a student, when uniform regulations were enforced with an iron fist.

"There's more embrace of kindness and autonomy, as well new gender dimensions that challenge traditional conceptions."

He hopes to see fewer schools enforcing hair length rules in future, and is optimistic about New Zealand's stance on gender roles.

"We're facing many of the same issues other countries are grappling with at the moment. These things aren't easy."