This study examines the links between students' families and science achievement across many countries. Science tests and questionnaire responses of 107,834 fifteen-year-olds in 41 countries were analyzed with multilevel analyses. Students had higher science scores if they were native born, lived with two parents, lived without grandparents, lived with fewer siblings (especially older ones), had more educational resources, had more family involvement, lived in wealthier countries, or lived in countries with more equal distributions of household income. In wealthier countries, family involvement, blended families, and number of siblings showed stronger links to science scores. Science achievement was more strongly linked to family socioeconomic status (SES) and educational resources in more egalitarian cultures and to single parents, family SES, resident grandparents, and birth order in more individualistic cultures. Hence, family constructs were linked to academic achievement in all 41 countries, and the links were stronger in more economically and culturally developed countries. Copyright © 2007 American Psychological Association.