Tracking is nearly ubiquitous in secondary schools despite evidence suggesting its general ineffectiveness and likely negative effects on students in low tracks. This paper, which originally appeared in Educational Psychology, v. 22, no. 2, April 1987, argues that two contexts in which tracking is embedded must be considered to understand how tracking works and why it persists. The schooling context (tracking's consequences for school and classroom practice) permits understanding of how tracking's educational effects may occur. The societal context (the beliefs, values, and circumstances that originally influenced the institution of tracking and may continue to shape the practice) provides an understanding of why tracking, and not some other approach, was adopted as the means for managing student diversity. It also provides insight into how race and class were historically confounded with tracking and may continue to influence practice. Analyses of these contexts suggest that tracking profoundly influences the day-to-day conduct of schools and reflects assumptions about how schools should respond to student diversity. This contextual view of tracking explains why tracking is not easily reconsidered.