Minority student attrition and underachievement is a long-standing and widespread concern in higher education. It is especially acute in introductory science courses which are prerequisites for students planning to pursue science-related careers. Poor performance in these courses often results in attrition of minorities from the science fields. This is a particular concern at selective universities where minority students enter with excellent academic credentials but receive lower average grades and have lower retention rates than majority students with similar credentials. This paper reports the first year results of a large scale peer-facilitated workshop program designed to increase performance and retention in Biology, Chemistry, and Physics at a selective research university. After adjusting for grade point average or SAT-Math score, workshop participants earned higher final grades than nonparticipants in Biology and Chemistry, but not in Physics. Similar effects on retention were found. While, positive effects of the program were observed in both majority and minority students, effect sizes were generally largest for minority students. Because of practical constraints in Physics, implementation of the program was not optimal, possibly accounting for the differential success of the program across disciplines.