Where did Sam Winchester go to college?
Keeping this in consideration, what was Sam Winchester studying in college?
Sam is studying for a law degree in the pilot episode of Supernatural, and he's looking at law schools while he's enrolled at Stanford. Later episodes would reference the fact that Sam was only in college for two years before he joined Dean in becoming a hunter.
Additionally, who does Sam Winchester end up with? In the year that Dean was stuck in Purgatory, Sam took up a relationship with veterinarian Amelia (Liane Balaban). The two lived together in Texas, dog and all.
Then, how long was Sam Winchester in college?
With this line of reasoning, Sam could not logically have been away for four years. This theory also takes into account the timeline of the pilot -- set at Halloween, Sam would only have been two months into his fourth year of college. This would mean that he has been at Stanford for three years and two months.
Who resurrected Sam Winchester in Season 6?
Sam has been resurrected by two Archangels: Michael and Lucifer. Even though he's had a stronger connection to demons, Sam is the only Winchester to become possessed by an angel twice. Once by the archangel Lucifer and the second time by Gadreel.