Three people have been arrested following a weapons complaint at Sudbury's Lasalle Secondary School. Police were called to the school at around noon.
A student reported to the main office that he was hit by a small object as he was walking across the parking lot behind the school.
The school was then locked down, and officials called police.
The school board said the student was not seriously injured, and police said the weapons being used were slingshots and paintballs.
A man and two male youths were arrested. Charges are still pending.
The lockdown was lifted at 1 p.m. once police confirmed it was safe.