Establishing an instrument's factorial invariance provides the empirical foundation to compare an individual's score across time or to examine the pattern of correlations between variables in differentiated age groups. In the recently published Woodcock-Johnson Tests of Cognitive Ability (WJ COG) and Achievement (WJ ACH) Third Edition (III) the authors provide evidence for the factor structure of the entire battery, but they did not report the formal testing of the factorial invariance of the battery across age groups. In practice, all WJ III tests are generally not administered to a single examinee. The purpose of this study was to investigate the factorial invariance of the WJ COG under one of the most frequent testing scenarios: the calculation of an examinee's General Intellectual Ability Score-Extended (GIA-EXT; a single, global or full-scale score of intelligence) and performance on the seven latent cognitive processing or Cattell-Horn-Carroll (CHC) clusters. The overall results from this study provide support for the factorial invariance of the WJ COG when the 14 tests contributing to the calculation of an examinee's GIA and CHC factors scores are administered. Support is provided for the WJ COG theoretical factor structure across five age groups (ages 6 to 90+ years).