This study examined how societal changes associated with modernization are related to cognitive development. Data were from 4 cultural communities that represented a broad range of traditional and modern elements: the Garifuna (Belize), Logoli (Kenya), Newars (Nepal), and Samoans (American Samoa). Naturalistic observations and the performances of 3-, 5-, 7-, and 9-year-old children (N = 192) on 7 cognitive measures were examined. Results replicated age-related improvement on all measures. Contributions of modernity were evident in children’s play behaviors and cognitive performances, especially in skills related to schooling. Modernization and schooling independently predicted differences on most of the measures. Results are discussed in relation to the Flynn effect, the worldwide increase in cognitive scores across generations, and the ways in which societal modernization may contribute to cognitive development.