Two students made the discovery in a computer lab, and they immediately told the librarian.
Officials say the students did not open the files, but spotted explicit titles in a shared folder.
The material was traced to the teacher and the laptop was turned over to Marple Township Police.
Nancy Caramanico, director of technology for Archdiocesan schools, says the school's acceptable use policy was violated and the students did the right thing by reporting it.
"This is all still under investigation," said Caramanico.
Not all of parents with whom we spoke had seen the initial e-mail from the school, but they were satisfied with the way the incident was handled.
The laptop has been sent to the state police in Harrisburg for a closer look.
Depending on the outcome of the investigation, the long time teacher could face charges.
