The Good Behaviour Game (GBG) is one of the most popular behaviour management systems for primary-aged children. It has an extensive evidence base supporting its use. The GBG itself can be described as an "interdependent group-oriented contingency management procedure." A major efficacy trial of the GBG in England was conducted that focuses on: (1) the intervention's effects on children's educational (e.g. reading, behaviour) outcomes; and in particular; (2) its impact on boys who are showing the early signs of behaviour problems; (3) children eligible for free school meals (FSM); (4) examining whether the way in which the GBG is implemented influences outcomes; and (5) whether the GBG improves outcomes for teachers (specifically, self-efficacy in classroom management, classroom stress, and retention). This study looked at 77 primary schools that were recruited from Local Authorities across the North West, South Yorkshire and East Midlands regions. This figure represents the number of schools required to power the trial plus additional schools to allow for attrition (see sample size calculations below). Schools were required to be state-maintained and not already implementing the GBG in order to be eligible to participate.