The study described in this paper utilized data from the National Assessment of Educational Progress (NAEP) to compare achievement trends among black and white students with respect to the variable of age at admission to first grade. The three age groups selected were nine, thirteen, and seventeen year olds. NAEP data in reading, mathematics, and science were combined and analyzed using multiple regression. Predictor variables included class age, relative age, sex, parental education, home environment, region, and type of community. It was found that by age seventeen, the differences between younger and older first grade entrants disappeared, but that trend differences persisted between white and black samples. It is argued that the change in whites is due in great part to higher retention rated among young males, and that for blacks there is a more general attrition phenomenon. (Author/GC)