Schools across the country are ending the practice of grouping students based on ability, in part, because of research indicating that tracking hurts low-ability students without helping students of other ability levels. Using a nationally representative survey conducted by the National Center for Education Statistics, (NCES) we reexamine the impact of tracking on high school student achievement through the estimation of a standard education production function. This approach allows us to control for the possibility that track is correlated with factors such as class size and teacher education. In addition, we address the possibility that there are unobserved student or school characteristics that affect both achievement and track placement. Our results indicate that abolishing tracking in America's schools would have a large positive impact on achievement for students currently in the lower tracks, but that this increase in achievement would come at the expense of students in upper-track classes.