Investigates the gap in math and science achievement of third- and fourth-graders who live with a single parent versus those who live with two parents in 11 countries. Finds single parenthood to be less detrimental when family policies equalize resources between single- and two-parent families. Concludes that national family policies can offset the negative academic outcomes of single parenthood. (Contains 63 references, 5 tables, 2 figures, and 1 appendix.) (GCP)