This longitudinal study assessed the effects of parents' marital transitions and pubertal development on grandparent-grandchild relationships. 9- to 13-year-old children, their mothers, and maternal grandparents from 186 Caucasian, middle-class families including 73 intact families, 64 mother-custody, single-parent families and 49 stepfamilies completed questionnaires focusing on the degree of children's “relationship involvement” (perceived closeness and frequency of contact) with maternal grandparents at 2 time periods 13 months apart. Children also completed questionnaires 9 months later during a third interview. Grandparents, and especially grandfathers, were more involved with grandchildren from single-parent families (supporting the “latent function” hypothesis). The pubertal status results supported the “emotional distancing” hypothesis for grandfather-granddaughter relationships (higher pubertal status, less involvement) and the “stress buffer” hypothesis for grandsons' relationships with both grandparents (greater change in physical development, more involvement and greater perceived closeness).