Results of community-based childhood obesity intervention programs do not provide strong evidence for their effectiveness. In this study, we evaluated the effect of the Thao-Child Health Program (TCHP), a community-based, multisetting, multistrategy intervention program for healthy weight development and lifestyle choices. In four Catalan cities, a total of 2250 children aged 8 to 10 years were recruited. Two cities were randomly selected for the TCHP intervention, and two cities followed usual health care policy. Children were selected from 41 elementary schools. Weight, height, and waist circumference were measured at baseline and after a mean follow-up of 15 months. Physical activity and adherence to the Mediterranean diet were measured with validated questionnaires. Generalized estimating equations (GEE) models were fitted to determine the intervention’s effect on body mass index (BMI) z-score, waist-to-height ratio, Mediterranean diet adherence, and physical activity. Fully adjusted models revealed that the intervention had no significant effect on the BMI z-score, incidence of general and abdominal obesity, Mediterranean diet adherence, and physical activity. Waist-to-height ratio was significantly lower in controls than in the intervention group at follow-up (p < 0.004). Conclusions: The TCHP did not improve weight development, diet quality, and physical activity in the short term.What is Known: • There is inconsistent evidence for the efficacy of school-based childhood obesity prevention programs. • There is little evidence on the efficacy of childhood obesity intervention programs in other settings. What is New:• This paper contributes information about the efficacy of a multisetting and multistrategy Community Based Intervention (CBI) program that uses the municipality as its unit of randomization.• This CBI had no effect on the prevention and treatment of childhood obesity in the short term.