Ch Insp Katie Rowland-Wilson, from South Yorkshire Police, said: “I want to make it clear that, although we are in the early stages of our inquiries, we have a boy in custody and we remain on scene to engage with the college community and offer our reassurances.
“We are now working to understand the full circumstances of what happened and we will remain in the area on our regular patrols.
“We understand news of this incident will cause considerable concern, particularly among parents and guardians.
“I’d encourage anyone who has concerns to speak to an officer when you see them and would urge anyone with information which could help our inquiries to report it to us.”
The college’s City Campus is located just a short distance from All Saints High School, where 15-year-old pupil Harvey Willgoose was stabbed to death in February.