Sex differences in the latent general and broad cognitive abilities underlying the Woodcock-Johnson Tests of Cognitive Abilities were investigated for children, youth, and adults ages 6 through 59. A developmental, multiple indicator-multiple cause, structural equation model was used to investigate sex differences in latent cognitive abilities as well as developmental changes in these differences across the 6 to 59 age span. Females showed a consistent advantage on the latent processing speed (Gs) factor, and males showed a small, consistent advantage on the latent comprehension-knowledge (Gc) factor. Males also showed an advantage on latent quantitative reasoning (RQ) and visual-spatial ability (Gv) factors at most ages, although the latter was statistically significant only for adults. No statistically significant sex differences were shown on latent auditory processing, short-term memory, long-term retrieval, or fluid reasoning factors. The higher-order, latent g factor showed inconsistent differences for children, small, non-significant differences favoring females for adolescents, and fairly consistent statistically significant differences favoring females in adulthood. Findings are inconsistent with developmental theory that suggests males should show an advantage on g in adulthood. Supplemental analyses suggested that methodological choices, including the use of latent variables versus composites and methods for dealing with missing data, can affect research findings. (Contains 10 figures and 9 tables.)