This is a first longitudinal study of parenting and stepparenting of siblings in divorced and remarried families over the postdivorce decade. Disparate parenting of siblings was evident in one half of the families. This was seriously and lastingly detrimental to the marginalized youngsters. The unexpectedly powerful influence of the stepparent on the parenting of the biological parents is reported along with the psychological role of children in reflecting the relationships and projections of parents and stepparents. The study raises clinical and theoretical questions regarding the roots of instability in parenting following disrupted and new adult partnering. The findings also call attention to the distinctive developmental pathways of children in divorced and remarried families.