A threat to stab a fellow student and a boast about being 'high' were posted in an online school group chat, with the academy investigating.
In a group chat on Microsoft Teams, which is accessible by the entire pupil population of The Holgate Academy in Hucknall along with teachers, the message 'I'll chef you up' was posted earlier in January this year.
That's slang for stabbing someone.
Another message said the poster was 'high'.
These messages were sent during school hours.
Teachers at the school are investigating, and believe student accounts could have been 'compromised', meaning the pupil named alongside the messages might not be the one that sent them.
Jay Pearce, 32, a single mum and hairdresser whose child attends the school, logged into Teams on her daughter's account which had access to the group chat, and saw the messages.
She said: "It's extremely concerning that this really, really, really explicit language could be seen by all.
"What else can I think? I know this sort of thing happens, I'm just concerned for my child's safety."
One of the messages also says 'get ur p***y bf then I'll stap him leave him', which Miss Pearce believes is another reference to stabbing someone with a typing error.
She said she reported the comments to the school as soon as she saw them.
Miss Pearce said: "There was a lot of teenage slang, but I saw the messages and reported them to the school straight away, but they were still up two or three hours later before they were taken down.
"The feature of that chat on Teams has now been blocked.
"On Facebook groups, there are features on there that can highlight certain words, but why is that sort of system not used here where my child can see all these messages?"
A spokesperson for The Holgate Academy said: "The use of our Teams environment, or on any platform, to post messages such as this is wholly unacceptable and our student community are fully aware of this.
"This is an ongoing investigation at the academy as we seek to determine who was involved in posting the messages.
"At this stage, we believe that student accounts may have been compromised and wish to make it clear that those students named on the messages may not have been responsible.
"If parents have any concerns at all, we welcome them to contact the academy for advice and support."
The incident was also reported to the police.
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