Physics Education Research focuses on improving the teaching of physics by understanding the cognitive mechanisms which either aid or hinder student learning, and developing pedagogical techniques to improve learning. Chandralekha Singh has led numerous studies documenting student difficulties in both introductory and advanced physics classes, and cognitive strategies for improving problem solving ability. The Singh research group has built and evaluated research-based tutorials for use in both introductory and advanced physics courses. The group also investigates innovations that can benefit the Department's and the University's teaching mission. Some examples are the establishment of the Physics Exploration Center, where students in introductory courses can experiment independently, the installation of student response systems (or clickers) in all four of the department's larger lecture halls, which enable the instructor to monitor student responses to questions posed during classes, and the construction of an introductory physics classroom designed to facilitate studio-style interactive teaching.