OBJECTIVE: The aim of this study was to evaluate the efficacy and feasibility of the Physical Activity Leaders (PALs) program. PALs is an obesity prevention program for low-active adolescent boys from disadvantaged schools. METHODS: The study was conducted in the Hunter Region, New South Wales (NSW), Australia from June to December 2009. Four disadvantaged secondary schools were randomized to treatment conditions for the 6-month study period. Participants were 100 adolescent boys [mean (SD) age=14.3(0.6) years; BMI=22.1kg/m(-2) (4.6); BMI z-score=0.6 (1.2)]. The primary outcome was change in BMI and secondary outcomes were body fat (bioelectrical impedance analysis), waist circumference, muscular fitness (leg dynamometer, 90 push-up test and 7-stage sit-up test), physical activity (5-days of pedometry) and selected dietary behaviors. RESULTS: Significant group-by-time interaction effects were found for BMI (mean difference=-0.8kg/m(-2), p<0.001, d =0.7), BMI z-score (mean difference=-0.2, p<0.001, d=0.7), and body fat (mean difference=-1.8%, p<0.05, d=0.5), but not for waist circumference, muscular fitness or physical activity. Participants in the intervention group reduced their consumption of sugar-containing beverages. CONCLUSIONS: The PALs program was a feasible and efficacious approach to induce healthy weight loss in adolescent boys from disadvantaged secondary schools. [ABSTRACT FROM AUTHOR]