This article compares the effects of family background and school resources on fourth-grade students' math achievement, using data from the 2011 Trends in International Mathematics and Science Study (TIMSS). In order to ameliorate potential floor effects, it uses relative risk and population attributable risk to examine the effects of family background and low levels of school resources. Four findings stand out: (1) the percentage of vulnerable students decreases as GDP increases, but this relationship weakens at higher levels of GDP; (2) the relative risk associated with low socioeconomic status is positively related to GDP, but the relative risk associated with low school resources is unrelated to GDP; (3) the population attributable risk associated with some of the family and school risk factors tends to fall with rising GDP, but varies considerably amongst countries; and (4) family background effects are stronger than school resource effects in low- and high-income countries.