This is a hands-on lesson that uses science and the steps of the Engineering Design Process to determine important properties in sail design materials and learn how to harness wind power. Students will learn that a problem can be solved in different ways using different materials, properties of materials change its effectiveness, conducting tests help determine versatility of materials, and that wind can be harnessed to do work. This lesson is adapted from Catching the Wind: Designing Windmills, Lesson 3: Testing Sail Designs (produced by the Museum of Boston for the Engaging Youth in Engineering program.) Visit http://www.mos.org/EiE for more information. This lesson plan was created as a result of the Girls Engaged in Math and Science, GEMS Project funded by the Malone Family Foundation.