Unit Overview In A Sticky Situation: Designing Walls, students discover and discuss the connections between the properties of earth materials such as clay, soil, and sand and their uses in engineering. The unit begins with the storybook Yi Min’s Great Wall, in which a girl named Yi Min living in China explores the field of Materials Engineering in order to build a wall to protect her garden from a hungry rabbit. Over the course of the unit, students observe and describe properties of earth materials both wet and dry, predict which materials will make the strongest mortar, and test their predictions. Like Yi Min, students then follow the steps of the Engineering Design Process to imagine, plan, create, and improve their own walls.