Paper to appear in the Proceedings of the Eleventh Conference on Research in Undergraduate Mathematics Education (2008). Explaining Student Success in One PDP Calculus Section: A Progress Report Aditya P. Adiredja , Randi A. Engle, Danielle Champney, Amy Huang, Mark Howison, Niral Shah, and Pegah Ghaneian, UC Berkeley In 1974 at UC Berkeley, many African American and Hispanic students were failing Calculus while most Chinese American students were successful (Treisman, 1985). Recognizing calculus as a gatekeeping course, Uri Treisman investigated the study practices of both groups. He found that while both attended the same lectures and worked equally hard on homework, the African-American and Hispanic students were academically isolated, while the Chinese- American students worked together on additional challenging problems (ibid.). In 1978, with Rose Asera, Robert Fullilove, Leon Henkin, Dick Stanley, and other members of the Professional Development Program (PDP) at UC Berkeley, he then created calculus intensive discussion sections for underrepresented students. The sections emphasized groupwork on challenging problems and a community based on shared interest in succeeding in mathematics (Asera, 2001; Fullilove & Treisman, 1990; Eric Hsu personal communication, February 2008; Treisman, 1992). Since then, students in PDP’s Intensive Discussion Sections (IDS) and similar programs elsewhere have outperformed comparable students in traditional calculus sections, and been more likely to successfully take additional STEM courses (Alexander, Burda & Millar, 1997; Chin et al., 2006; Fullilove & Treisman, 1990; Kosciuk, 1997; Moreno & Muller, 1999; Moreno et al., 1999). As a result of this success, colleges and universities around the country have sought to use the IDS model on their own campuses. Although some adaptations of the model (like those cited above) have been highly successful, others have not (Asera, 2001; Hsu, Murphy &