formulation of geometry, whereas, so Hestenes asserts, the term “Clifford algebra” is often regarded as simply “just one more algebra among many other algebras”, which withdraws attention from its role as a unified language for mathematics and physics. Hestenes' work has been applied to Lagrangian field theory, formulation of a gauge theory of gravity alternative to general relativity by Lasenby, Doran and Gull, which they call gauge theory gravity (GTG), and it has been applied to spin representations of Lie groups. Most recently, it led Hestenes to formulate conformal geometric algebra, a new approach to computational geometry. This has found a rapidly increasing number of applications in engineering and computer science. Modeling theory and instruction Since 1980, Hestenes has been developing a Modeling Theory of science and cognition, especially to guide the design of science instruction. The theory distinguishes sharply between conceptual models that constitute the content core of science and the mental models that are essential to understand them. Modeling Instruction is designed to engage students in all aspects of modeling, broadly conceived as constructing, testing, analyzing and applying scientific models. To assess the effectiveness of Modeling Instruction, Hestenes and his students developed the Force Concept Inventory, a concept inventory tool for evaluating student understanding of introductory physics. After a decade of education research to develop and validate the approach, Hestenes was awarded grants from the National Science Foundation for another decade to spread the Modeling Instruction Program nationwide. As of 2011, more than 4000 teachers had participated in summer workshops on modeling, including nearly 10% of the United States' high school physics teachers. It is estimated that Modeling teachers reach more than 100,000 students each year. One outcome of the program is that the teachers created their own non-profit organization, the American Modeling Teachers Association (AMTA), to continue and expand the mission after government funding terminated. The AMTA has expanded to a nationwide community of teachers dedicated to addressing the nation's Science, Technology, Engineering, and Mathematics (STEM) education crisis. Another outcome of the Modeling Program was creation of a graduate program at Arizona State University for sustained professional development of STEM teachers. This provides a validated model for similar programs at universities across the country. Awards and fellowships 2014 Excellence in Physics Education Award from the American Physical Society 2003 Award for excellence in educational research by the Council of Scientific Society Presidents 2002 Oersted Medal, awarded by