The impact of collaboration and communication among 5-9 year olds on their cognitive development was explored in the course of 3 experiments. Children worked on a task either as individuals or in pairs. Each child's partner thought about the task at the same level as him, at a higher level, or at a lower one. When no feedback was provided (experiments I and II) only children whose partners reasoned at a higher level were likely to improve. Those whose partner reasoned at a lower level declined more than all other children. The same pattern of results was obtained in an American and a Russian sample (experiment II). When feedback from the task materials was provided however (experiment III), individuals improved more than pairs. These results are discussed in terms of Piagetian and Vygotskian theories.