Four series of studies focus on identification and treatment of hyperactive children. One focus is the specification of the precise behaviors-in-context that distinguish hyperactive from nonlabeled children. Another, broader focus is on the cognitive, behavioral, and situational concommitants of psychostimulant treatment. A major aim is to specify the subecologies in which children are most likely to be perceived hyperactive and to delineate the behaviors which engender the label. A second goal is delineation of the psychosocial and cognitive sequelae of medication and assessment of their impact on the subsequent behavior patterns of the child and her/his significant others. One set of quasi-naturalistic classroom studies will compare hyperactive and normal children as incremented degrees of structure are imposed on their tasks, the physical contexts, and their social encounters. The next studies use multimodal assessment of identified children and their families before and during the initial months of psychostimulant therapy. Acute drug response studies will be done but the major focus is on the causal constructs developed by the children and their parents as these constructs predict both immediate and long-term outcomes of psychostimulant therapy. The third empirical goal is an assessment of immediate and long-term effects as hyperactive children reach adolescence and medication is discontinued. A fourth research series will assess inference processes and individual differences in adults, especially teachers, in the identification of hyperactive behaviors. The research program has numerous theoretical aims. The most central is to test the functional efficacy of recent developments in cognitive (attribution and expectancy) theories.