Data from the standardization sample of the Woodcock–Johnson Psychoeducational Battery–Third Edition (WJ III) Cognitive standard battery and Test Session Observation Checklist items were analyzed to understand the relationship between g (general mental ability) and test session behavior (TSB; n = 5,769). Latent variable modeling methods were used to construct both the g and TSB factors, and measurement invariance of the two latent factors was tested across five age groupings (ages 6-8, 9-3, 14-19, 20-39, and 40+). Results indicated partial scalar invariance across age groups for both the g and TSB factors. Correlations between the g and TSB factors were moderately strong and statistically significant across all groups. Suggestions for future research that is most likely to advance theory development and scale development related to the relationship between g and TSB are discussed.