PARENTS OF 27 BOYS WHOSE AGRESSIVE OR DEVIANT BEHAVIOR HAD LED THEM TO BE LABELED 'PREDELINQUENT' WERE REFERRED TO THE SOCIAL LEARNING PROJECT AT THE OREGON RESEARCH INSTITUTE BY COMMUNITY AGENCIES. AT THE PROJECT THESE PARENTS WERE TRAINED IN SOCIAL LEARNING TECHNIQUES OF CHILD MANAGEMENT. TRAINED OBSERVERS WENT INTO THE HOMES OVER A 12-MONTH PERIOD TO OBSERVE THE EFFECTIVENESS OF THE NEW TECHNIQUES OF CHILD MANAGEMENT. THIS HOME OBSERVATION DATA SHOWED THAT AGGRESSIVE BEHAVIOR FOR THE TREATED BOYS DROPPED SIGNIFICANTLY BELOW .450 AGGRESSIVE RESPONSES PER MINUTE, THE MOST EFFICIENT CUTTING SCORE FOR DIFFERENTIATING SUCH BEHAVIOR. HOWEVER, THESE OBSERVATIONS ALSO SHOWED CHANGES IN SIBLING BEHAVIOR. DURING BASELINE OBSERVATIONS DEVIANT SCORES FOR THE PROBLEM CHILDREN WERE .795, FOR THE SIBLINGS .563. BY THE END OF THE STUDY DEVIANT BEHAVIOR SCORES FOR BOTH SIBLINGS AND PROBLEM CHILDREN HAD DROPPED TO UNDER .390. COMPLETE 12-MONTH FOLLOWUP WAS AVAILABLE FOR 16 FAMILIES. IN THESE THE CHANGES IN SIBLING BEHAVIOR CONTINUED TO IMPROVE. IT IS SUGGESTED THAT OFTEN AGGRESSIVE BEHAVIOR IN THE 'PROBLEM' CHILD IS TRIGGERED BY THE SIBLING AND, CONVERSELY, A PROBLEM CHILD TRIGGERS AGGRESSIVE BEHAVIOR. IT IS APPARENT THAT THE PARENTS WHO RECEIVE THE INTERVENTION TRAINING LEARN A SET OF SKILLS WHICH THEY CAN APPLY TO ALL THEIR CHILDREN AND THAT INTERVENTION WITH ONE CHILD CHANGES THE WHOLE FAMILY SYSTEM.