She is a 14-year-old student.
But, they never crossed paths, until he allegedly found her on MySpace.
Police sources say the teacher courted the girl on her MySpace web page.
They say he eventually convinced her to go with him to his apartment in Allentown.
That's where they allegedly engaged in sexual activity.
Police say it had been going on for two weeks before they realized that he is a teacher and she is a student at the same school.
When the girl's mother found out about the alleged affair, she called the police.
Police have searched the teacher's apartment and they've confiscated his computer.
They've also sent a subpoena to MySpace to track all of his activity on the social networking website.
The Philadelphia School District acted swiftly when it became aware of the police investigation.
Police have taken DNA samples from both the alleged victim and the teacher. It may take a couple of weeks before they get lab results.
The school district isn't saying where the teacher might have been posted prior to his current assignment at South Philadelphia High. Although, public records indicate he taught at West Philadelphia High School four years ago.
The police are trying to determine if there might be other victims.
