The effects of peer interaction as it relates to equilibration in the development of map drawing activity was studied in 72 fifth graders. The children were pretested and placed into 36 same sex pairs for training on the basis of Piaget and Inhelder's six-stage sequence of map drawing ability. A discrepancy (above, below or at the same stage) between each subject's pretest modal stage and a partner's modal stage was used to define an external disequilibrium condition for each subject. To explore relationships between peer interaction and developmental change, an observer coded utterances between partners and assigned each pair an involvement rating. An observation system permitted subjects' overt behavior during exposure to external disequilibrium to be related to changes on posttests. Results confirmed a significant effect of discrepancy between peers at differing stages in promoting developmental change. External disequilibrium due to developmental differences between partners both within and between stages produced similar patterns of change. Pair involvement rating and frequency of on-task discussion were also found to be significantly related to advance. (Author/SS)