Background: Value-added modeling (VAM) has been used to rank teachers and assess teacher and school quality. The apparent relationship between value-added teacher rankings and gains in student performance provide a foundation for the view that the contribution of teachers to student performance is the largest factor influencing student achievement, suggesting that differences in teacher quality might explain the persistence of the gap in student achievement as students advance throughout the K-12 years. However, several studies raise questions about the reliability and validity of VAM. Purpose: The purpose of this article is to reconcile the evidence that the contribution of teachers to student achievement is large with the evidence that value-added rankings are unreliable and possibly invalid. Design: The method involves an analytical review of the available evidence, development of a theoretical explanation for the contradictory results, and a test of this explanation using path analysis with three longitudinal datasets involving nationally representative samples of schools and students. Conclusion: The hypothesis that the contribution of teachers to student performance is the strongest factor influencing student achievement is not supported. A stronger factor is the degree to which students believe that they are proficient students. This is consistent with the view that the persistence of the achievement gap is better explained as the outcome of structural factors embedded in the conventional model of schooling that undermines the self-efficacy, engagement, effort, and achievement of students who enter kindergarten performing below the level of their more advantaged peers.