This study examined how resources, distribution inequality, and biases toward privileged students affected academic performance. Fifteen-year-olds from 41 countries completed a questionnaire and tests in mathematics, reading, and science. Multilevel regression analyses showed that students scored higher in all subjects when they had more resources in their country, family, or school. Students in countries with higher inequality, clustering of privileged students, or unequal distribution of certified teachers typically had lower scores. Distribution inequality favored privileged students, in that schools with more privileged students typically had more resources. Overall, students scored lower when parent job status had a larger effect on student performance (privileged student bias) in a school or country. These results suggest that equal opportunity is linked to higher overall student achievement. (Contains 1 note, 3 tables and 1 figure.)