Effectiveness of a universal classroom-based preventive intervention (PAX GBG): A research protocol for a matched-pair cluster-randomized controlled trial.

Introduction: The PAX Good Behavior Game (PAX GBG) is a universal classroom-based program that promotes children's mental health. In Estonia, the intervention is delivered to first grade students (aged seven to eight) within the regular school curriculum. The current work describes a protocol for a cluster-randomized controlled trial (RCT) of the PAX GBG conducted in Estonia.