Over the past two decades the University of California at Berkeley has been actively engaged in improving undergraduate education in science and mathematics. As a part of these efforts, the Professional Development Program has created the `Intensive Discussion Section` (IDS) model for mathematics. These IDSs, which emphasize active student learning of course material at a high level, as well as collaborative efforts and good communication skills, have proven highly successful in advancing certain underrepresented groups through introductory calculus courses. The IDS model has recently been adopted in physics and chemistry for underrepresented students as well, with the same success. A two-year pilot program is proposed to begin expanding these IDSs for all students in lower division physics, chemistry, and mathematics, and at the same time to improve cross- disciplinary exchange among these subjects. These changes will require creation of new course materials and improved graduate student instructor training. Coupled with other ongoing curriculum reform at Berkeley, these improvements are expected to greatly improve student achievement in these gateway courses, to improve student performance and retention in upper division coursework, and to produce graduates well matched to the needs of employers in science, engineering, technology, and other disciplines. This proposal represents the first attempt to institutionalize academic reform in lower division at a major research university. The results will be thoroughly evaluated and disseminated widely.