Aim <p>This study aimed to evaluate the effectiveness of a school-based multimodal intervention targeting healthy lifestyle behaviours among schoolchildren in the province of Cádiz.</p> Subject and methods <p>A quasi-experimental design was employed, comparing outcomes between the experimental and control groups. The intervention adopted a multimodal approach, targeting students, their families and educational institutions. The students participated in a healthy educational programme of 10 sessions and were provided with two workbooks to use at home with their families. Additionally, parents attended three training courses aimed at improving their children’s lifestyle behaviours. The intervention aimed to achieve significant improvements in various health-related parameters such as body composition, physical fitness, physical activity levels, sedentary behaviours, dietary patterns and sleep pattern.</p> Results <p>The results suggested that the intervention produced moderate and at times variable effects in promoting healthier lifestyle behaviours among schoolchildren. While improvements were noted in the experimental group compared to the control group, these did not fully meet the initial expectations.</p> Conclusions <p>This outcome underscores the need for further research and adjustments in implementation, such as the integration of specialized external personnel to support teachers, embedding the intervention into the school curriculum and extending its duration throughout an entire academic year. This study contributes valuable insights into childhood obesity prevention and intervention strategies, paving the way for future research endeavours aimed at promoting the health and well-being of children worldwide.</p>