Students and staff were placed in a lockdown situation for about an hour yesterday after reports of someone carrying what turned out to be a replica firearm.
It happened just before the noon hour.
OPP Acting Sergeant Anne McCoy says it ended without incident.
A 16-year-old boy was taken into custody away from the high school and the replica firearm seized.
The Fort Frances High School and the Rainy River District Board is offering support to students to help cope with the incident.
They are making counsellors available.