Within the framework of research into the effectiveness of psychological treatment, meta-analysis has become a complementary procedure to the traditional reviews that help to interpret large amounts of data. The interest aroused by this methodology has led to studies focused on different areas of behavior and health sciences. In this article, the standard phases of a metaanalytical review are discussed. Meta-analysis principles of the overall effectiveness of psychological treatment in childhood are reviewed. Results show that treatment effectiveness reaches an overall effect size above the mean and comparable to that obtained by meta-analysis in treatment with adults. The effectiveness of behavior therapy for specific problems such as depression or enuresis is analyzed and an average effectiveness is gained in the majority of psychological disorders. The effectiveness of behavior treatments in other areas such as teenage delinquency, chronic illnesses, child operations, family therapy and prevention programs are also considered.