For almost a century, schools have assigned students to various groups or classes based on their perceived academic ability. Referred to as Tracking, in the United States, and Streaming, in England, this organizational differentiation very often results in unequal access to knowledge and the differential treatment of students. Proponents of tracking contend that it facilitates instruction and promotes the learning of all students. They suggest that it enables teachers to adjust the content and quantity of the curriculum to the various ability levels of their students. Notwithstanding the research which underscores the negative impact of tracking on student outcomes, this practice remains pervasive in schools and a number of assumptions support its popularity. This article examines these assumptions in light of existing English and American research to determine, once and for all, if tracking is a positive form of educational differentiation or a defective strategy.