Children's groups are a traditional subject matter in developmental psychology. One of the more salient features of such groups is social structure. In his review of the literature, Hartup (1970) said of such organization that "individual differences inevitably produce differentiation of status positions; children's peer groups always possess a hierarchical structure, " and that " ... status differentiation is a universal attribute of group functioning [po 370, emphases added]. " But, although Hartup 's review is excellent in every other respect, in dealing with this topic, he makes little reference to the nonhuman primate literature on peer influence. Our thesis, to the contrary, is that a fuller understanding of important aspects of the structure and functioning of children's groups depends on a systematic comparative assessment of similar features in nonhuman groups. We finnly believe that animal data of this sort make an important contribution to mainstream developmental psychology. But, what is the proper place of these data in our discipline?