We focus a LOT on our writing skills in my class. I try to challenge them and shake things up when I can. This is one of my favorite ways to do that. They are used to me providing the beginning of the story with a prompt...instead, I give them the ending. My favorite ones to do are "and then we had a pet", "and then the cookies were gone" and "then there was a knock at the door". I posted this idea before and Ian Byrd from the Byrdseed site http://www.byrdseed.com/ commented that he liked to give that last prompt idea as dealer's choice-they could use it at the beginning of their story or at the end.
So these are their stories about disappearing cookies: