Background Although various hypotheses have been offered to explain the racial achievement gap between White and Black students, conventional theories that focus on the quality of schools, teachers, or a child's home environment are unsatisfactory. Instead, the available evidence points to a new theory. Purpose The purpose of the study was to evaluate the new theory against this evidence and to compare the explanatory capacity of this theory with the explanatory capacity of three conventional theories of the racial achievement gap. Sample/Design/Analysis Analyses of data from the nationally representative Early Childhood Longitudinal Study of the Kindergarten Class of 1998 (ECLS-K) were combined with results from studies that suggest how the hypothesized mechanism operates to maintain and perpetuate differences in achievement that exist at entry into kindergarten, plus results from randomized experiments that test hypothesized theoretical relationships. Results The results suggest a pattern of puzzling empirical results that are difficult to reconcile except in terms of the new theory. Conclusion The evidence points away from conventional theories regarding the achievement gap and toward the new theory.