Earth Day Escapade

Who rained on the parade?River Heights Elementary School is putting on an Earth Day parade, and Nancy's class has a special honor: They get to build the float! Nancy, Bess, George, and all the kids in Mrs. Ramirez's class have worked hard to make the "greenest" float they can, collecting recycled materials to use for decoration.
But someone's spoiled all the fun and sabotaged the float days before the parade. Who could've done something like this -- and why? Sounds like another case for the Clue Crew!