How exactly does a 3-D printer work? You can ask the students at Glen Grove Elementary School, who are using one to solve potential urban problems. The students are taking part in the City X Project, an international educational program that challenges kids to come up with ideas for new devices that could help the imaginary residents of City X. The students use tablets to design their objects, then make models out of clay. Then they can use the 3-D printer to create real plastic prototypes. The kids at Glen Grove, outside of Chicago, are working on a device that would clean up a river after an oil spill, for example, and a pair of headphones that a city dweller might use to dampen urban din. The overall goal of the City X program is to use technology to teach students valuable problem-solving skills. It’s not only a great way to get students thinking and learning about design, but also to prepare them to work with the cities and technology of the future. Watching the kids build their models layer by layer with the 3-D printer, one teacher described it as the “coolest thing in the world.”