This study examined how well adults can make inferences about children's cognitive abilities. Subjects (n=60) were four groups of adults: female parents, female nonparents, male parents, and male nonparents. They were shown the typical method of administering 13 Piagetian tasks, ranging from object permanence to the formal-operational pendulum task. For each task, subjects were asked about average age of mastery, variability in speed of development, possible sex differences, and developmental origins of the concept. Responses to the age question showed a tendency to overestimate ages for the developmentally earliest concepts and to underestimate ages (in some cases quite markedly) for the developmentally later concepts. Subjects were nevertheless fairly accurate in dating many concepts; they were also quite successful at identifying sequences in development, positioning a reversal in only 9 percent of the cases. Responses to the remaining questions varied to some extent across concept; subjects' general tendency, however, was to deemphasize sex differences and variability and to rate self-discovery as the most important contributor to development. Few differences between males and females or parents and nonparents were founded. (Author/RH)