From elementary school to midlife: Childhood personality predicts behavior during cognitive testing over four decades later

•Child Big 5 personality and adult behavior during cognitive testing was examined.•Evidence for personality stability with teacher ratings and observed behavior.•Child Openness relates to a number of task relevant behaviors.•Openness relates to adult behavior even when controlling for cognitive performance.•Child Conscientiousness weakly relates to behavior and not as expected. The current study uses a prospective, longitudinal design and lifespan perspective to understand how child personality relates to directly observed adult behavior during cognitive testing. Teacher assessments of child Big Five personality in elementary school were correlated with directly observed behaviors during a videotaped cognitive test four decades later. Past work suggested Openness and Conscientiousness may relate to task-relevant academic behaviors. Childhood Openness was associated with several behaviors, even after controlling for participant’s cognitive performance. Childhood Conscientiousness was also related to behavior, but not as expected. Other Big Five ratings were not reliably related to behavior. The study examined personality stability in a unique way and suggests a further examination of how Openness in children manifests in later behavior.