A while back ago I found a fic where Dean was in highschool, and I'm going to assume that in the later chapters, it reveals that Castiel is, too. At first, Dean explains that Sam (who is currently out of the picture) is "coming home" from somewhere, and hints that he may have been sick or have had mental problems in the past. He then later talks about how Sam always insists that he go to school and get a decent education (possibly because he isn't getting one himself due to his poor health and constant need of medical attention?). Dean is just about to go to his school, remembering that Sam is in fact coming home today, and he'll be upset if he sees that Dean has yet to leave. But just as he's walking out of the doorway, Sam shows up. Dean gives him a small tour of the house, explaining that it's Bobby's, and that John has yet to show up. After school, Dean heads to a bar where Ellen works, gets drunk, and starts to make his way back home. He's confronted by Crowley and Gabriel (highschoolers, I suspect), and is attacked. Castiel comes to the rescue, and brings Dean home. End first chapter.
All of the characters that show up in this one chapter are:
Sam, Dean, Castiel, Crowley, Gabriel, Ellen, and Jo, with mention of John, Bobby, and possibly Mary.