Video has been circulating online showing an alleged assault on a teenage boy outside the Anderson High School in Lerwick.
Police said an alleged assault had been reported at around 10am on Thursday.
“We are also aware of a video circulating online regarding to this incident,” a force spokeswoman said.
“Enquiries are continuing.”
The incident follows escalating concerns about bullying, violence and drugs at the school.
As reported in this week’s edition of The Shetland Times, a group of parents have written to senior staff calling for firm action to tackle the problem.
The SIC’s children’s services director Helen Budge said: “We take any concerns such as these very seriously and the safety and welfare of young people in our schools is our absolute priority.
” We’re unable to comment on any individual circumstances but can reassure parents and carers that our schools have well established procedures and frameworks to tackle these issues, with links to Police Scotland and other local agencies where necessary.
“If they have any concerns, parents and carers of young people should contact their school in the first instance to discuss these.”