Streets are closed, students are locked down or sheltered in place and bomb-sniffing dogs are brought in. Sometimes parents become fearful and converge on the school.
It happened three times in Bergen County this past week.
Hackensack High School was targeted twice, once prompting a brief evacuation and another time a shelter-in-place.
It happened again on Friday, April 1 at Ridgewood High School.
"A male caller called the main police number spoke with central dispatch and stated he was distraught from breaking up with his girlfriend and placed explosive devices by the entrance of the high school" on Friday morning, Ridgewood Police Capt. Forest Lyons said.
Investigators haven't said whether they believe the calls are being made locally or by a "swatter" in another state -- or country.
"Swatting" incidents peaked nationwide about five or six years ago before subsiding somewhat. They have since flared up again.
Ridgewood High School was placed in moderate lockdown following Friday's call, Lyons said.
The school was searched, the threat was deemed unfounded and the day quickly returned to normal. Village police kept parents and residents apprised via social media.
The Bergen County Sheriff's Bomb Squad and K-9 Unit were among the responders.
Ridgewood police and the Bergen County Prosecutor's Office were investigating.
Click here to follow Daily Voice Highland Lakes-Vernon and receive free news updates.