In this action research study, research findings related to developing children's prosocial behavior were discussed at a seminar with parent/teachers in a cooperative nursery school to determine if post-seminar parent/teacher intervention would lead to increased prosocial behaviors in the children. Forty-seven children in the nursery school were divided into four classes and their prosocial behavior was assessed. Parent/teachers from two classes (one group of 3-year-olds, one group of 4-year-olds) participated in a 2-hour prosocial development seminar. Parent/teachers from the other two classes functioned as a control group. In the seminar group, research findings related to prosocial modeling, role playing and other techniques were discussed. Praising naturally occurring prosocial behaviors and emphasizing preferred rather than disapproved behaviors were encouraged. For seven weeks, experimental group parent/teachers kept logs of classroom interventions done as a result of the seminar. Post-intervention test results indicated significantly more (p < .01) prosocial behavior for experimental over control children. Data were analyzed with three-way analysis of variance followed by Scheffe multiple comparisons. It was concluded that theory and experimental findings in prosocial development can be applied to the natural preschool setting with positive results. (Author/RH)