In the spring of 1960, the authors conducted a countywide study of the 875 children in the third grade (modal age of 8 years) of all public and private schools. In the first wave, the major variable of interest was aggressive behavior in school and at home. Aggressive behavior at school was measured with a peer nomination technique administered to children in their classrooms. Data on other variables were obtained from the children at this time; most of the parents were interviewed with a precoded schedule. In the second wave, conducted 11 year later (modal age of 19), 427 of the original subjects were retested. Another peer nomination inventory yielded aggression measures on the subjects. Other tests were administered to measure aggression in other ways. The third wave, administered 11 years later (modal age of 30 years), involved 409 of the original subjects. In addition to measuring aggression for these subjects, data were obtained on these subjects and 223 others from mental health, motor vehicle, and criminal justice records. Data indicate that aggression is at least partly learned from the interaction of the person with the environment, although genetic predisposition to more or less aggression is likely. 6 figures, 2 tables, 94 references.