The procedures by which children from lower and middle class backgrounds attempt to obtain rewarding outcomes from each other were observed under semicontrolled conditions. Ten male and 9 female dyads, each composed of 1 middle class and 1 lower class preschool child, were required to complete 12 simple block puzzles in which each was given some of the pieces his partner needed. Rewards were given for cooperative or competitive performance. "S"s in the two socioeconomic groups demonstrated similar behavioral repertoires. Their behavior usually involved the physical manipulation of puzzle pieces, rather than attempts to influence their partners. About 3/4 of all observed interpersonal acts could be categorized into taking, delivering, and demanding puzzle parts. Middle class "S"s were more successful in general, but their demands were complied with less than were those of lower class "S"s. When competitive conditions were first, "S"s emitted more acts in both payoff conditions than when cooperation was first. This effect was strongest among lower class girls, possibly because of dominance of female models in the lower class home environment. A followup study on 2 very low performing lower class subjects revealed that their responsiveness increased greatly when paired with familiar lower class partners in their own preschool environment. (Author)