The family structure in which children and adolescents grow up is related to their educational achievement. However, this relationship is mediated to a significant degree by the resource allocation of different family constellations. A detailed analysis of these relationships is still lacking, partly because the family structure is often not recorded in a sufficiently differentiated manner. Using data from the National Educational Panel Study (NEPS), this article examines how families with two biological parents, stepfamilies, and families with single mothers or fathers differ in terms of endowment with (socio-)economic, cultural, and social capital, and how this affects the reading and math skills of their children in the 9th grade. Our analyses show that mainly cultural capital, and to a lesser extent (socio‑)economic and social capital, are responsible for the reading and math skills in the 9th grade. Families with both biological parents have the highest resources, whereas single-parent families command significantly fewer resources, with differences observed between single fathers and single mothers. Nevertheless, not all differences in educational achievement between children in different family structures can be attributed to resource differences: especially children who live together with single fathers perform significantly worse in the competence tests, even after controlling for resources.