Ottawa police have arrested a 15-year-old boy in connection with one of 18 prank 911 calls in the past month that have prompted police to lock down numerous high schools across the city.

They are also pursuing other "persons of interest" to determine who is responsible for false reports of people carrying guns at Ottawa schools, police Supt. Charles Bordeleau told a news conference Friday afternoon.

Police locked down three Ottawa schools Friday and five others the day before responding to 911 calls that turned out to be hoaxes. Calls leading to other lockdowns since Sept. 21 were similarly false, Bordeleau said.

"No weapon or intruder has been found in any of these situations," he said. "However, this is not a victimless crime. Allegations of such incidents occurring in schools are very stressful for all those involved."

Such incidents are frustrating school staff and students, as well as police, said Dan Wiseman, the safe-schools manager for the Ottawa-Carleton District School Board.

People need to understand how gut-wrenching the situations are and how much fear they conjure up these days among those involved, he told CBC's Ottawa Morning on Friday.

The hoaxes come at a time when there have been a number of high-profile shootings at North American schools and colleges, including one that killed Grade 9 student Jordan Manners in a Toronto high school in May.

The incidents also put a strain on the city's police service, he added.

"You can imagine this is having a tremendous effect on their resources on an ongoing basis," Wiseman said, adding there is a very set procedure that police and schools have to follow in response to such calls.

"It's a very well-orchestrated, well-practised, very intrusive, I might say, intervention," he said.

But it is necessary under the circumstances, he added, and despite the high number of false alarms, police and school officials can't and won't ignore or underrespond to such situations.

"The margin of error, when you're dealing with a life-threatening situation, is zero."

Wiseman said police are actively investigating the hoaxes, and the school board hopes parents, students or other members of the public will come forward with information about the incidents and who might be responsible.