Intergenerational relations have received close attention in the context of population aging and increased childcare provision by grandparents. However, few studies have investigated the psychological consequences of becoming a grandparent. In a preregistered test of grandparenthood as a developmental task in middle and older adulthood, we used representative panel data from the Netherlands (N = 563) and the United States (N = 2210) to analyze first-time grandparents’ personality and life satisfaction development. We tested gender, employment, and grandchild care as moderators. To address confounding, we employed propensity score matching using two procedures: matching grandparents with parents and nonparents to achieve balance in different sets of carefully selected covariates. Multilevel models demonstrated mean-level stability of the Big Five personality traits and life satisfaction over the transition to grandparenthood, and no consistent moderation effects—contrary to the social investment principle. The few small effects of grandparenthood on personality development did not replicate across samples. We found no evidence of larger inter-individual differences in change in grandparents compared to the controls or of lower rank-order stability. Our findings add to recent critical re-examinations of the social investment principle and are discussed in light of characteristics that might moderate grandparents’ personality development.
