The flier was read by some parents as excluding all other ethnicities and girls.
"Imagine if you had've done the same thing and said white boys only what the hue and cry would be," said Whanganui resident Tony Greig.
Greig was speaking for his neighbour who was a student at the school and was keen to attend the Parker session, but didn't want to speak out for fear of being victimised.
"It's nothing short of racism and sexism and that's defined by omitting someone by the colour of their skin to an event or work or anything.
"It's sexist as well because girls can't go, and there are a lot of girls interested in boxing and who would be keen to listen to Joseph Parker talk. He's a pretty influential fella."
There was further outcry online with a Facebook page hosting numerous comments opposed to the event being exclusively for Maori and Pasifika boys.
Parker's promoters, Duco, said they were baffled by the itinerary and said it was the first they had heard of it.
"We're very surprised to hear this is going on and, if it is the case, Joseph won't be attending because that's not something he would support at all," the spokesman said.
"That's not Joseph; that's not how he operates."
According to the flier, Parker's itinerary started with a powhiri, and then presentations by Māori and Pasifika student leaders before the motivational talk.
Whanganui High School principal Martin McAllen said it was possible Parker would be available for further public events that anyone could attend, but he wasn't sure.
McAllen and board of trustees chairman Randal Southee said the request had come from Parker for the talk to be closed and they were happy to oblige.
McAllen said he'd had only a few concerns raised about the talk being for just Māori and Pasifika boys.
"I don't understand why there would be any concern with it ... because so many initiatives within schools are focusing in on Māori and Pasifika students.
"This is a real case of rather than just talking about it, actually walking it in terms of appreciating the opportunity we've been given and then being able to facilitate that."
However, board of trustees member Piri Cribb said the request for a closed session had not come from Parker's camp.
When asked why the school had said that, she replied: "Probably because that's the easiest way to combat some of the horrible feedback and flak that they're getting about the closed session.
"It's very difficult to combat the reverse racism statements, the exclusive, the elitist statements that the school is currently succumbing to."
Cribb was adamant it was an opportunity to focus on a section of students who were less engaged.
"I'm very clear, as one of the people sorting out the visit for Joseph Parker to our school ... we have a responsibility to provide some culturally relevant and appropriate opportunities for our Māori and Pacific Island boys whom we fail dismally — not just at Whangnaui High School but as a country to engage in our education system.
"Joseph Parker's visit is an opportunity to do that.
"It's not a separatist movement and it's not an elite strategy ... it is simply an opportunity to capitalise on the cultural similarities that this man has with our young men."
Cribb said the school didn't have the capacity to hire a hall and open the talk up to more students.
"It's down to resources and space and I'm happy to say it is also down to the priorities at our school."
She said if the talk was cancelled amid the outcry she would take responsibility for the decision she was a part of.
"Then I'll be very sad for those young men."
