When I clicked on this I hadn't checked the genre, so I didn't know it was a crossover until I read the A/N. Then I figured I might as well give it a go, I know absolutely nothing about Supernatural but your story looked interesting.
You do have an interesting plot here. I haven't read too many crossovers, but to me this seems like a good way to cross worlds in a fairly plausible way. I came here because the summary suggested something new, and you're off to a good start. You've clearly established the two main characters you're dealing with, you've introduced at least two possible romances, and you've given us a good idea of what we can expect Sam and Dean to do here. I liked the fact that they had a classroom as headquarters, an office for a bedroom and got majorly lost, because all of those seem realistic of a first-time stay at Hogwarts.
However, I'd like to offer some CC as well. The readability of the story could be improved, specifically regarding the dialogue. From the first few words spoken I could tell that you were not a fan of the word "said," and were going to search for alternatives to it. In the end, you only used it five or six times in a story with a lot of dialogue. But the the thing with those alternatives is that if they're used to heavily, they seriously detract from the story as the reader begins to get distracted. "Said" is expected, you see, so the eye skims right over it. Other words are louder and more visible, so too many of them make us pause and wonder why the story isn't flowing so well. Does that make any sense? Obviously the exact variations you choose to use are personal preference, but in my opinion you were a bit heavy here. In particular, the use of the word "stated" made for some awkward wording.
Also concerning dialogue, I spotted some grammatical errors. When writing dialogue, a comma always comes before the last quotation mark (unless it's a question mark or an exclamation point), otherwise you're left with a sentence fragment for your speech tag. For example, "'I don't know but the one is really dreamy.' Ginny stated" should be: "'I don't know but the one is really dreamy,' Ginny stated." There's more on the in the Writer's Resources section of the forums.
Other than that, you're off to a good start. You certainly caught my attention with this first chapter, and having no experience with Supernatural or crossovers did not affect my read at all.
Author's Response: Well, thank you for reading this. I'm glad you enjoyed it even though you know nothing about Supernatural.
I'm glad you liked the possibility of the love interests and everything else. I'm glad you think it is plausible.
As for the stated, replied, or whatever, I had an English teacher in high school who told us not to use said all the time because it's typical, it's boring. She said to spice it up a bit and so that's what I've done. As for the comma after the dialogue, I was also taught to do it that way. You put a comma if they're not done speaking, but if it's the end of their speech, you put a period. I could be wrong, but oh well.
I did write this ages ago too, so I can go back through and fix some things.
Thank you again for the review.