Children who experience lone motherhood differ from children who remain with both biological parents before family transitions occur, complicating observed family structure gaps. Using the Children of the NLSY79, we estimate a dynamic model of family arrangements, financial resources, parental investment, and child skills with persistent family heterogeneity. A transition into lone motherhood at age 7 generates a persistent resource decline and gradually widening skill differences, reducing schooling and adult wages. A Shapley decomposition attributes about 94 percent of the adult effects to the resource-to-skill pathway. Complementary counterfactuals show that timing and persistence shape the developmental consequences of family change.