This cross-cultural, developmental study of understanding of the physics of a balance scale involved 2 age groups (5- and 22-year-olds) in 2 countries (the United States and Zimbabwe). A factorial design was used. Each participant solved 6 types of balance scale problems, and the patterns of errors for these problem types were analyzed to determine which rules and concepts the participant used (e.g., whether number of weights was considered). As expected, on average, older participants were more accurate than younger participants, although significant age differences in the Zimbabwean sample were not found for problems solved by weight or distance cues. One finding differing from earlier research was that problems in which the beam balanced were more difficult for all participants. Generally, understanding of the physics of a balance scale appeared fairly similar in the 2 countries. Some cultural practices may account for the findings--in particular, the availability of preschool and age at time of academic specialization in higher education.