This article reports on an innovative approach to teaching Calculus I which was initiated in a two-semester course designed for students at risk of failing Calculus I. The treatment consisted of voluntary oral assessments offered before every written examination. Analyses showed that the treatment students did significantly better than the control group on course grades as well as a common final exam that tested both concepts and procedures. Treatment students designated at-risk due to their placement scores at the outset of the course, completed Calculus I, were retained at the university, and enrolled in and passed Calculus II at dramatically higher rates than at-risk students in the control group. Subsequently, orals have been introduced in large lecture classes with promising results. (Contains 5 tables and 2 figures.)