This study examined how a contextual approach to child assessment can clarify the meaning of informant discrepancies by focusing on children's social experiences and their "if...then" reactions to them. In a sample of 123 children (M[subscript age] = 13.30) referred to a summer program for children with behavior problems, parent-teacher agreement for syndromal measures of aggression and withdrawal was modest. Agreement remained low when informants assessed children's reactions to specific peer and adult events. The similarity of these events increased consistency "within" informants but had no effect on agreement "between" parents and teachers. In contrast, similarity in the pattern of social events children encountered at home and school predicted informant agreement for syndromal aggression and for aggression to aversive events. Our results underscore the robustness of informant discrepancies and illustrate how they can be studied as part of the larger mosaic of person-environment interactions. (Contains 5 footnotes, 2 tables, and 3 figures.)