Background and aims: Therapists has considered the play therapy as an effective intervention for behavioral problems of children. The aim of this research is to study the effectiveness of school-based group activity play therapy on behavioral problems among preadolescents' male students from shahrekord.

Methods: A quasi experimental field design with pretest, posttest and control and placebo groups using the multistage random sampling method for each of the experimental, placebo and control groups, 15 participants (45 in total) were selected. For assessing the behaviorial problems, teachers report form was used. The experimental group received 16 sessions of group activity play therapy during 8 weeks and the placebo group received 16 sessions of instructions and competitive play. The control group received no intervention. Data were analyzed using multivariance covariance.

Results: The results showed that play therapy based on group activity caused a reduction in internalizing behavioral problems on experimental group, but had no significant impact on the reduction of externalizing behavioral problems.

Conclusion: Based on play therapy literature and the findings of this research, it is suggested that the educational system of Iran acts on establishing play therapy centers as one of the most effective counseling and psychotherapy interventions for children in the elementary schools.