Parents are getting aggressive with teachers when their child has a problem at school - and both the number of incidents and the level of vitriol is on the rise, says John Collier, the head of St Andrew's Cathedral School in Sydney.

Parents are getting aggressive with teachers when their child has a problem at school - and both the number of incidents and the level of vitriol is on the rise, says John Collier, the head of St Andrew's Cathedral School in Sydney.

Recently, Collier wrote about the issue in a school newsletter, and his message has gone viral.

An increasing number of parents are delivering tirades as facts, shouting at school staff "as their opening gambit" and sending strident emails, he tells Kathryn Ryan.

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Collier is Head of School at Sydney's elite St Andrew's Cathedral School and has been a school principal for 28 years.

He says while most of the St Andrew's parents are "lovely", teachers there are sometimes shouted at (in parent-teacher interviews, problem resolution meetings and over the phone) and sent emails containing an "onslaught" of capital letters or exclamation marks.

In the newsletter, Collier uses the word "reptilian" to describe their knee-jerk, accusatory instincts.

This aggression, he believes, is fuelled by increased anxiety from today's "frenetic pace of life", as well as media coverage of sportspeople and celebrities normalising aggressive behaviour.

Parents of a single child can become overinvested in their success, and, in the case of "fairly affluent" St Andrew's parents, high fees can go along with an inflated sense of entitlement, Collier says.

He tells Kathryn Ryan parents can react aggressively to how the school responds to a "minor disciplinary infraction", lower test or assessment marks than they believe their child is due and even the homework their child is set.

One accused the 13 staff members who saw his daughter involved in a bullying incident of lying.

When parents adopt this "siege mentality" - and defend their child come what may - it gives "emerging adults" the wrong message and renders impossible the reasonable, respectful interchange needed to solve problems, he says.

Media outlets in England, Brasil and France have now picked up the story, and Collier says he's also had an enormous show of support from St Andrew's parents, teachers and principals at other schools, and people working in the retail and health industries.

"I assume what I've done, inadvertently, is touched a chord in society about the increasing incivility of public discourse."

Go to this episode on rnz.co.nz for more details