I've heard that agents/editors dislike prologues (usually, I think, in submissions as it doesn't show a true sense of the tone/style of the book).
I've gone back and written a prologue in my story because whether it becomes MG or YA, I think I've got to show at least a hint of how dark the novel will become. Now, usually even I hate prologues--I skimmed the ones in the Twilight series, I skip most of the ones in epic fantasy tomes (they're just going to reveal a prophecy or something anyway). So I guess I'm being a bit hypocritical, writing a prologue...
...but it is the perfect answer to my worry that the overall tone of the book is hidden by the mild opening, and it gives some insight to the villain's character.
What's y'all's opinion on prologues?
PS: My mother, who has no idea about my angsty-decision for MG or YA, just sent me an email in response to my question on whether or not my ms. was more for middle school kids or high school kids. Her words: Aren't they both the same??? :)