One-quarter of the Head Start population has a mother who participated in the program as a child. This study uses experimental Head Start Impact Study (HSIS) data on 3- and 4-year-olds (N = 2,849) to describe multigenerational Head Start families and their program experiences. In sharp contrast to full-sample HSIS findings, Head Start has large, positive impacts on cognitive and socioemotional development through third grade among the children of former participant mothers, including improved mathematics skills and reductions in withdrawn and aggressive behavior. Evidence suggests that differences in program impacts between single- and multigenerational Head Start families are driven largely by differences in family resources and home learning environments. (author abstract)