ABSTRACT
In recent years, psychologists and psychiatrists in the field of Attention-Deficit/Hyperactivity-Disorder [ADHD] have been research doing for measurement of validity and efficiency of available treatment and. In this regard, meta-analysis integrates the results of different studies then determines the effect size of drug treatment. This study seeks to investigate the effective rate of methylphenidateon on reducing ADHD symptoms by following the meta-analysis model. 21 Studies which were methodologically accepted were selected and meta-analysis was done on them. The research tool was meta-analysis check list. The result indicated that rate of effect size drug treatment on reducing ADHD symptoms was 0.71 [p