Invitation to Invent, a physical science unit for grades 3-4, engages students in investigations and observations that support their learning about simple machines and their uses. Students explore force, motion, and friction as they learn about the six simple machines and how they are put together to form compound machines.Invitation to Invent was developed by the Center for Gifted Education at The College of William and Mary to offer advanced curriculum supported by years of research. The Center's materials have received national recognition from the United States Department of Education and the National Association for Gifted Children, and they are widely used both nationally and internationally.Each of the books in this series offers curriculum that focuses on advanced content and higher level processes. The science units contain simulations of real-world problems, and students experience the work of real science by using data-handling skills, analyzing information, and evaluating results. The mathematics units provide sophisticated ideas and concepts, challenging extensions, higher order thinking skills, and opportunities for student exploration based on interest. These materials are a must for any teacher seeking to challenge and engage learners and increase achievement.Grades 3-4