The purpose of this research was to investigate the cognitive abilities that explain reading comprehension across childhood and early adulthood. Drawing from the standardization sample of the Woodcock-Johnson III, analyses were conducted with large samples at age levels spanning early childhood to early adulthood: 5 to 6 (n = 639), 7 to 8 (n = 720), 9 to 13 (n = 1,995), 14 to 19 (n = 1,615), and 20 to 39 (n = 1,409). Using a model including factors representing general intelligence, Cattell-Horn-Carroll broad abilities, and reading decoding skills, results revealed significant direct effects for reading decoding skills and Crystallized Intelligence on reading comprehension across all age levels. Memory-related abilities, processing speed, and auditory processing demonstrated indirect effects on reading comprehension through reading decoding skills. The magnitude of direct and indirect effects varied as a function of age. The results provide support for integrative models of reading that include both direct and indirect effects of cognitive abilities on reading comprehension and for consideration of developmental differences in the cognitive aptitudes predicting reading comprehension. (Contains 5 tables, 1 figure, and 8 footnotes.)