A study was made to examine effects of peer collaboration on children's cognitive development and to ascertain whether effects of collaboration varied across American and Russian cultures. A total of 84 girls and boys (42 from a kindergarten in Moscow and 42 from an elementary school in Ithaca, New York), 5 through 7 years of age, initially participated individually in a pretest requiring prediction of the way a beam would tip when different weights were placed at differing distances from a fulcrum. On the basis of pretest results, children were assigned to (1) a control group in which children were again tested individually; (2) an "equal rule" group pairing same-age, same-sex children who had used the same prediction rule on the pretest; or (3) an "unequal rule" group pairing same-age, same-sex children who had used different prediction rules on the pretest. Seven increasingly sophisticated rules for prediction have reliably been differentiated. In the treatment phase of the study, disagreeing subjects discussed their disagreement until agreement was attained. Subjects were individually post-tested and improvement in rule use was recorded. Findings indicated that cognitive conflict in pairs produced different outcomes depending on whether a child's partner was more advanced or less advanced in the use of prediction rules. The only differences across cultures were sex differences. (RH)