To test the hypothesis that cultural diversity contributes to the development of formal reasoning, samples of adolescents from three predominately white middle-class communities located in areas that varied in the extent to which they offered cultural diversity (i.e., rural, suburan homogeneous, suburban heterogeneous) were administered a test of formal reasoning and a test of analytical intelligence. Results showed significant differences in formal reasoning in favor of the suburban heterogeneous sample on complex reasoning items. The suburban groups showed equal performance (but superior to the rural Ss) on the test of analytical intelligence. On the less complex reasoning items and on one item embedded in a rural farming context, the rural Ss showed relatively better performance. Implications for using science instruction to promote formal reasoning are discussed.