A Short Message Service programme was adapted to monitor three health behaviours and provide supportive feedback. The study aimed to evaluate the effectiveness of the programme to increase fruit/vegetable consumption and physical activity and to decrease screen time. A total of 139 Portuguese children, aged 8–10 years, grouped by classroom, were randomly assigned to an intervention (8 weeks of monitoring/feedback) or a control condition. Participants had their key behaviours assessed at baseline, post-intervention and follow-up. A three-level hierarchical linear model was developed. Results showed that the monitoring and feedback programme significantly increased fruit and vegetable consumption over time.