Arrange students in groups of three or four and have them decide if they’d rather design a roller coaster or a waterslide. Discuss what fun, thrilling elements their design should have (its criteria) and its limitations (e.g., materials and time to make the design). Have students sketch a design and share it with you. Then they can build a model of their ride, using simple materials like tape, scissors, cardboard tubes, construction paper, and paper cups. Have students test their designs with marbles, then have them make improvements. Finally, have them present their final design to the class.