Since school-based interventions are mainly delivered by the school staff, they need to be well-trained and familiarized with the programme's aims, procedures and tools. Therefore, the institute, research group, governmental or non-governmental body in charge of the coordination and implementation of the programme needs to devote time and resources to train the school staff before programme's implementation. This is particularly crucial in multi-centre studies where more than one research teams are involved. Both research teams and school staff need to be trained, using standard protocols and procedures, to ensure that the intervention will be delivered in a standardized manner throughout the intervention centres. The ToyBox-intervention, a multi-component, kindergarten-based, family-involved intervention, focusing on water consumption, snacking, physical activity and sedentary behaviours in preschool children, was implemented over the academic year 2012-2013 in six European countries. As part of this intervention, three teachers' training sessions were delivered to motivate and train teachers in implementing the intervention. The local researchers were trained centrally before delivering the training sessions for the teachers and followed a common protocol using standardized presentations and procedures. The aim of the current paper is to describe the protocol and methodological issues related to the teachers' training sessions conducted within the ToyBox-intervention. (author abstract)