PROCEDURE: 72 children 1/2 boys, 1/2 girls (4 years). 3 conditions and all children matches on initial aggression. One group - watched aggressive model his bobo doll with a hammer + punch saying boom, pow. Second group - watched non-aggressive model that played quietly in corner of the room. 3rd group had no model (control group) left in the playroom with bobo doll and observed through 1 way mirror for 20 min.