We are experiencing a technology shift: powerful and easy-to-use touchscreen-based mobile devices such as smartphones and tablets are becoming more prevalent than traditional PCs and laptops. Many mobile devices are going to be the first and, in less developed countries, possibly the only computing devices that virtually all people would own and carry with them at all times. We propose to reflect this new reality in how computer science is taught in the classroom. In this tutorial, participants will learn about developing software directly on smartphones without a PC using TouchDevelop on Windows Phone, a novel application-creation environment from Microsoft Research. Its typed, structured programming language is built around the idea of using only a touchscreen as the input device to author code. Easy access to the rich sensor and personal data available on a mobile device results in a fun and engaging programming experience for students.