This study examined the impact of culture, language, and familiarity with materials on the ability to solve traditional conservation problems. A total of 80 Tzeltal speaking children from two traditional Mexican Indian (Mayan) villages participated in the study: 5 boys and 5 girls drawn from each of four age group (6-7, 8-9, 10-11, 12-13). The men in both villages are agriculturalists; the women in one village are potters and in the other village they embroider blouses. Conservation of continuous quantity was examined using beans, clay, and water. Conservation of weight was studied using clay. Each child completed all tasks. Analysis of the data suggests that the ability to make conservation judgments improves with age among Mayan children as it does elsewhere in the world, but that performance lags behind U.S. norms by about 3 years. Language and culture differences which may explain this apparent performance lag are described. It was concluded that the conservation paradigm may not be a "culture free" test of cognitive competence. (ED)