S04E13: 'After School Special'

Sam and Dean take a trip down memory lane when they head to their old high school to investigate the murder of a popular student.

A second attack leads the brothers to believe that a disgruntled ghost is possessing the weaker members of the school and using them to inflict punishment on the campus bullies.

The Winchesters suspect that the culprit is an old friend of Sam's who was tormented so relentlessly that he killed himself on the school grounds.

However, the investigation takes an unexpected twist when Sam finds himself to be the next victim and the the boys begin to think they might not have the right suspect.

Elsewhere, the brothers flashback on their own, very different, experiences at Truman High, which leads Sam to question a very big decision in his life.