Background/Context: Despite decades of research, the persistence of the gap in student achievement between disadvantaged minority students and their middle-class peers remains unexplained. Purpose/Objective: The purpose of the current article is to propose a new model of the achievement gap. Research Design: Data were analyzed from three nationally representative data sets: The Early Childhood Longitudinal Study of the Kindergarten Class of 1998-1999 (ECLS-K), the National Education Longitudinal Study (NELS), and the Education Longitudinal Study of 2002 (ELS). Findings/Results: The achievement gap may be explained as a consequence of the conventional structure of schooling and the failure to individualize task difficulty and provide performance feedback in a way that is necessary to ensure that all students experience mastery. Many students become disengaged and the effect is most severe for disadvantaged minority students. Alternative theories of the achievement gap do not adequately explain the observed pattern of data. A league table analysis indicates that interventions based on the proposed model of the achievement gap are more efficient than 21 alternative approaches for raising achievement and suggest a promising strategy for addressing the achievement gap.