The incident prompted a lockdown and an early dismissal on Tuesday. School officials say it all began when information was received about two separate threats made to the school.
Police say those threats involved an explosive device and a possible weapon.
Police were notified and, on their advice, the school was placed on lockdown.
Officers, including a K-9 unit, inspected the building for any dangerous devices. No devices were found and no injuries were reported.
Eventually, it was decided that students should be dismissed as a precautionary measure, and students went home shortly after 12 p.m.
On Tuesday night, police announced the arrest of a juvenile.
"It was an emotional day for all of us especially for the students and staff. I applaud how my officers and the school district administration, students, and high school faculty staff handled this situation," said Chief Daniel Friel with the Warrington Township Police Department.
Student Shirley Haro said at first many students thought the morning lockdown was just a drill. But then...
"The principal said through the announcement that it was actually something going on," she said. "Everybody started freaking out when they saw the police and they said the K-9 was coming."
The incident left some parents unnerved. Jim Warrington says he received two emails from the school describing the situation.
"That's when my wife called me and said, 'go pick up our daughter,'" he said.
Mill Creek Elementary School nearby was also placed on lockdown for a short time because of its proximity to the high school, but those students were not dismissed early.