Researchers and anti-bullying organisations have increasingly turned their attention to the role of bystanders in tackling bullying and peer victimisation (e.g. name-calling). The objective of this study was to develop and assess the impact of a role-play programme designed to strengthen adolescent's defending behaviour to name-calling. This was measured in two contexts: defending intentions in an outgroup name-calling scenario and cyber-defender behaviour in a scripted online peer interaction. Participants (N = 121, M[subscript age] = 12.90 years) were randomly assigned to either a role-play condition or a control condition. Results showed that defender intentions in an outgroup name-calling scenario were higher in the role-play condition, compared to the control; in addition, cyber-defender behaviour was more likely and quicker in the role-play condition, compared to the control. Defender self-efficacy was found to be significantly higher in the role-play condition, and mediated the effect of the role-play programme on defender intentions. Findings also revealed that defender intentions were positively correlated with cyber-defender behaviour, highlighting a link between intentions and behaviour. Implications for theory and practice are discussed.