Police said the lockdown was invoked just before 1 p. m. when staff from the Ontario Street secondary school told Halton police a male teen inside the school was armed with what appeared to be a BB gun or air pistol.

An arrest was made a short while later.

A spring-loaded airsoft BB gun was seized, said Sgt. Brian Carr of Halton Regional Police.

A police investigation revealed the air pistol was discharged at a student earlier that morning in the school. The 17-year-old victim received very minor injuries and required no medical attention.

Carr said the air pistol appears to have been shot as “more of a prank” and not maliciously.

“It’s not the same calibre as a pellet gun,” Carr said, adding he still wouldn’t want to be on the receiving end.

Students were let out of their classrooms at about 1:30 p. m.

A letter from school administrators went home with students Wednesday explaining the situation to parents, said Marnie Denton, manager of communications with the Halton District School Board.

The letter was also to be posted on the board’s website.

“We want to make sure there’s clear information to parents about what happened and what didn’t happen,” she said.

Denton outlined the board’s lockdown procedure, in which students are kept in their classrooms and the doors are locked from inside the rooms. Nobody is permitted to leave the class until the principal gives the okay, she said.

A 16-year-old Milton male has been charged with assault with a weapon, carrying a concealed weapon and possessing a dangerous weapon. He was released to his parents Wednesday.

Stephanie Hounsell can be reached at sthiessen@miltoncanadianchampion.com .