Police say the 15-year-old gun buyer seemed to think owning a gun would be cool, while the 15-year-old seller has significant mental health issues.
"There's nothing to indicate any type of threats for any type of problems, absolutely none," said Superintendent Michael Chitwood of the Upper Darby Police Department.
Police were called around lunchtime Monday after a fellow student saw one teenager with a stun gun. He reported it immediately.
Security was alerted and found the teenager had apparently brought to school two guns, a .25 caliber semi-automatic and a .38 caliber revolver, both with ammunition, along with a knife and a stun gun.
However the question remained - where was the .38 caliber revolver that the bullets belonged to?
Police soon found that the gun had been sold earlier to another teenager for the stun gun and $100.
Both weapons had been stolen from family members of the seller without their knowledge.
In a statement to parents, the district said, "Thanks to a tip from a student, our school security was able to search and seize the weapons from both of the students before any open threat of violence took place."
"We need adults to act like adults and lock up these weapons and not make keys available to children," said Louis DeVlieger, Superintendent for the school district.
When asked about the need for metal detectors, the school superintendent says in the past he has spoken to security experts who advised they would have no use given the design of building.
School district officials say that counselors will be at the high school for any students who would like to talk.