Dr. Seth Hornstein is a senior instructor in the Department of Astrophysical and Planetary Sciences (APS) at the University of Colorado at Boulder since January 2007. He earned a B.S. in physics from Virginia Tech in 2000 and his Ph.D. in astronomy from the University of California, Los Angeles in 2006. At CU, his primary responsibilities involve contributing to the teaching reform of the large (~200-student enrollment) introductory courses. He has already found unique ways to transform these large courses into more learner-centered environment through the use of Peer Instruction with clickers, classroom discussions, and Lecture-Tutorials. He serves as a mentor for undergraduate APS majors with career interests in teaching and is the department coordinator for the Learning Assistant program (a university-wide program to recruit and prepare talented science majors for careers in teaching). Since 2008 he has been working with the Center for Astronomy Education's Collaboration of Astronomy Teaching Scholars (CATS) team leading a program to develop a Solar System Concept Inventory for use in intro solar system courses.