At just after 1.30pm, officers were called to reports of a boy being stabbed at Milton Keynes College, Chaffron Way.
Emergency services treated him at the scene before taking him to Milton Keynes General Hospital, where he died.
The boy’s next of kin have been informed and they are being supported by specially trained officers.
The thoughts of everyone at Thames Valley Police are with the family of the victim.
An 18-year-old man from Milton Keynes has been arrested on suspicion of murder.
There is a large police cordon, which is likely to be in place for some time.
If any members of the public have concerns, please do not hesitate to speak to one of our officers.
Anyone with any information about the incident should call 101 or visit our website, quoting reference 43220064415.
If you do not wish to speak to police you can report 100% anonymously through the independent charity Crimestoppers on 0800 555 111.