One place to look for this type of information is in the Front Matter of each Unit, on the page called Overview (I-12 in 5th grade). Although they are not called prerequisites, the information in the Connection to Other Units section provides some ideas about the background your students should have/will need. For example, Kids, Cats, and Ads strongly suggests that students have had The Shape of the Data from 4th grade, and adds that 3 Out of 4 Like Spaghetti is also good preparation. If you know fourth grade teachers have not taught one or both of these units, you will need to plan accordingly. (Hopefully those books are available/accessbiel to you!)
Also see Chris Van Laanen's Jun 14 post (Ivestigations and Ex-Ed) about using Student Activity Booklets from the grade level or two below you to support students who are struggling.
