Halifax Regional Centre for Education says the lockdown at Dartmouth High School has been lifted.
The high school was placed on lockdown Wednesday afternoon while Halifax Regional Police investigated a weapons complaint.
"Police completed building search and have determined students can safely be dismissed," said HRCE on Twitter.
It added delays are expected with student transportation.
Police have a 15-year-old male in custody and say they recovered an imitation handgun at the scene.
No one was hurt in the incident.
The investigation is ongoing and officers remain on scene as of 6 p.m.
Victoria Rd. has now reopened to traffic.