Pediatric obesity has become a global pandemic in the last century, contributing to short and long-term medical conditions that heighten the risk of morbidity and mortality in children. The 12-month school-based obesity management educational program aims to assess the effect of adherence to the lifestyle educational program and target outcomes, obesity, and hypertension. A total of 363 (nonadherent, N = 179; adherent, N = 184) Saudi school adolescents aged 12–18 were recruited from 60 schools in Riyadh City, Saudi Arabia. Anthropometrics, lipid profile, and blood glucose were measured at baseline and post-intervention. The level of adherence was based on the number of attended educational sessions, and participants were grouped accordingly into two groups: adherent group (attended ≥ 3 sessions) and nonadherent group (attended 1–2 sessions) out of a total of five sessions. Results demonstrated that significantly more participants in the adherent group achieved the primary program goal of reducing obesity indices [body weight, body mass index (BMI), and BMI z-score] than the nonadherent group. Additionally, among adherent obese participants, BMI z-score significantly decreased after the 12-month intervention (post-intervention: 1.5 ± 0.7 vs. baseline: 1.7 ± 0.6, p < 0.05), while the trend in BMI z-score modestly increased in the nonadherent obese participants post-intervention (post-intervention: 1.8 ± 0.7 vs. baseline: 1.7 ± 0.6, p > 0.05). Moreover, there was a substantial reduction in hypertension prevalence only in the adherent group (p = 0.003) and among adherent obese participants in particular (p = 0.03). Furthermore, adherence to session attendance was higher in girls than boys, which led to better outcomes among girls than boys. For the secondary outcomes, lipid profile indices increased in both groups, while no changes were observed in the glycemic profile. In conclusion, greater adherence to educational sessions achieved modest but favorable weight changes and improved blood pressure among obese adolescents. Future intervention studies should take into consideration the need to improve attendance to enhance adherence to the program among adolescents at risk.