OBJECTIVE: This trial aimed to determine if return rates of consent forms for vaccination could be improved when Vaxcards were offered as an incentive to school children. SETTING: Nineteen schools in South East Melbourne participated. INTERVENTIONS: Students in the experimental arm received a pack of Vaxcards when they returned their government consent form. OUTCOME MEASURES: Return of 'yes' consent forms for vaccination as part of a local government council vaccine programme was the primary outcome of this trial. Return rates were compared between the intervention and control schools and with historical return rates. RESULTS: Secondary school students (N=3087) from 19 schools participated. Compared with historical returns, a small global reduction in 'yes' responses to consent forms of -4.21% in human papilloma virus consent 'yes' responses and -4.69% for diphtheria, tetanus and pertussis was observed across all schools. No difference between the experimental and control groups was observed. CONCLUSIONS: Low 'yes' consent rates and reduction in consent rates between 2018 and 2019 for all groups are concerning. This finding highlights the need for behaviour change interventions across all groups to increase vaccine confidence. Lack of effect of incentivisation with Vaxcards in this study may have been due to the timing of receiving the cards (after the decision to vaccinate had been made, not before) and the limited intensity of the intervention. Optimising the timing and the intensity of exposure to Vaxcards could improve the outcome. TRIAL REGISTRATION NUMBER: ACTRN12618001753246.