Longitudinal data on the auditory forward and backward digit span (FDS and BDS) subtests of the Wechsler Intelligence Scale for Children (WISC) were obtained at five age levels (between 6 and 13), in samples of white and black children. Factor analysis and analysis of variance of the data were conducted to test 5 hypotheses, related to Jensen's Level I - Level II theory: (1) FDS and BDS involve different components of cognitive ability; the former reflects rote learning and memory, the latter reflects complex cognitive processes; (2) BDS is more highly loaded on g, the general intelligence factor, than is FDS; (3) whites and blacks show a larger average difference in BDS than in FDS; (4) the difference between FDS and BDS decreases with increasing age (or mental maturity); and (5) whites and blacks of the same WISC mental age perform the same on both subtests. All of these hypotheses were supported, although results were not always consistent at every age level. (Author/CP)