A spokeswoman for the Catholic Diocese of Maitland-Newcastle said the school's investigation had found the students had breached various policies, procedures and values.

"All five students have been suspended for 20 days and following this, two students will face expulsion if they have not withdrawn their enrolment from the school," the spokeswoman said.

The boys were also interviewed by a police liaison officer and are not allowed to attend the year 10 retreat.

A spokeswoman for NSW Police said its investigation had not identified any criminal offences and the police school liaison officer was working with St Pius X to address the matter.

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The diocese spokeswoman said the five students - as well as three students who don't attend Catholic schools - "created a list of girls they liked in an Instagram chat".

"There was no identifying title to this list, nor any comments referring to what the list was for," the spokeswoman said.

She said allegations received by the Newcastle Herald that the list was a "rape list" were not correct.

"NSW Police did not identify the list as a 'rape' list or consider that any of the students named on the list were at any risk," she said.

She said a year 10 male student had raised the alarm.

"A St Pius X High School student was unintentionally copied into the thread and, upon realising the nature of the content, reported it to a teacher at the school," she said.

"The teacher then immediately reported the contents to one of the school's assistant principals."

She said 72 screenshots were provided to NSW Police, which she said had confirmed none of the screenshots or images were child abuse material.

"However, two of the images were deemed 'inappropriate,' and both were of males," she said.

"The photos are described by NSW Police as 'one of the images is naked but from the back, so only the bottom is in view, and the one front photo the genital area has been blurred out'."

Director of Cyber Safety Solutions and former police officer Susan McLean said it was good to see a school act promptly and send a clear message the behaviour was not acceptable.

She said the student who reported it was a "rare breed".

She said while there may not be any child abuse material, online conversations could be a serious matter if they constituted the crime of using a carriage service to menace, harass or cause offence.

She said people could be charged from the age of 10.

"If you're repeatedly talking about one of the girls that could be harassing," Ms McLean said.

"There are certainly crimes. If one girl is mentioned multiple times that could be stalking offences.

"There is this unwillingness from victims to come forward and there is this unwillingness of police to actually do what they should be doing."

Ms McLean said student conversations and lists about girls and their appearances had become common over the past five years and came in different forms.

She said she'd previously seen hot or not lists and online conversations that asked students to upload photos of girls they found attractive at their and nearby schools.

One even asked boys to upload photos of their formal dates.

The boys couldn't bring the girls unless their friends rated the girls a nine or 10.

"There are those hot or not lists everywhere, they circulate all the time, they are abhorrent," she said.

"It shows a distinct lack of respect of those boys towards those girls.

"The problem is those girls have to go to school with those boys moving forward, that makes it very, very, difficult.

'They [schools] need to be doing better because prevention is always better than cure. I don't want young women to think this is their lot in life, that they have to accept being on these lists.

"They need to have courage to come forward and make reports. I want to see [more] boys breaking ranks and calling out the appalling abhorrent behaviour of their mates.

"[Hot or not lists] are typically sexist behaviour and it's that locker room banter, if you like, that is now taking place in the public domain, that's what they need to understand.

"It is there, it is there forever, it can be traced, someone might have a screenshot of it and throw it back at you when you're applying for a job in five years time."

A school parent who spoke to the Herald anonymously said St Pius X families were "greatly concerned".

"It does not leave you with a very comfortable feeling about sending your kids to school," the parent said.

"I don't know how the parents of the boys were involved... you'd be absolutely ropeable, you don't understand how in this day and age something like that can happen, it just shows complete and utter lack of respect."

The parent said the girls had not been aware of the conversation or what had been said about them.

"It was pretty unnerving and a lot of the girls were pretty upset and very shaken... they were not sure why it was happening and a lot of them wanted to know if they'd done something wrong."

School principal Robert Emery wrote to parents on the last day of term one about a "false rumour" circulating.

"A private, social media group-post involving some students from St Pius was uncovered on a social media site," he wrote.

"In that group post was a list of students, the purpose of the list is unclear.

"The material associated with the list has been reviewed by police and they are satisfied that there is no evidence of malice or ill intent attributable to the list.

"The Office of Safeguarding has been advised.

"From the start of term two, the school will conduct further investigation into other material posted by the group which may constitute a breach of school rules.

'St Pius X High School has zero tolerance for any forms of coercion or bullying. No form of sexualisation or objectification of a student by another student, or anybody else, will be tolerated within the school community.

"We ask you not to listen or pass on rumours, as it may cause distress to members of our school community. Students are safe at our school."

The parent said Mr Emery's letter "inflamed the situation".

"We were all pretty angry," the parent said.

"I could not believe how dismissive and vague it was... it was upsetting," they said.

Several families expressed their concerns to the school during the holidays.

Mr Emery wrote to families again on April 22, saying police had "determined there was no evidence of criminal intent associated with the website".

"In the second week of the school holidays, the police provided the school permission to commence its own investigation into whether our own policy and procedure had been compromised," he wrote.

He said St Pius X continued to work on its culture.

"As our community is aware, we have been working on improving school culture by educating students in the dignity of each human person and building respectful relationships," he wrote.

"We encourage all families to have regular and open conversations about these issues... our hope is through education and support there are positive changes in attitude and response to these issues."

Ms McLean said schools needed comprehensive cyber safety education and behaviour change programs delivered by experts.

"Parents need to step up to the plate and adequately parent in the digital space as well."

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