## 3 Results
### Study Characteristics
#### 3.3.2 Qualitative Synthesis  
Study design and population characteristics demonstrated substantial heterogeneity that directly influenced intervention effectiveness patterns. Six studies implemented longer interventions lasting \(\geq\)12 months [40; 41; 42; 44; 49; 51], while five used 6-9 months [43; 45; 47; 48; 50] and one used 20 weeks [46], with sample sizes ranging from 61 [51] to 8573 participants [41] across ten countries. Studies with longer durations (\(\geq\)12 months) [40; 41; 42; 44; 49; 51] produced more consistent improvements across multiple biomarkers compared to shorter interventions (6-9 months) [43; 45; 47; 48; 50]. Intensity-based subgroup analysis showed that high-intensity interventions with \(\geq\)4 sessions per week [47; 50] achieved larger effect sizes for anthropometric and blood pressure outcomes, while moderate-intensity approaches with daily brief activities [41; 48] produced significant but smaller effects across larger populations. Short-duration, high-intensity interventions [47; 50] were particularly effective in targeted populations, whereas longer-duration, moderate-intensity programs [41; 42; 44] showed sustained benefits in general school populations, suggesting that intervention design should match population characteristics and implementation capacity. Population targeting strategies varied fundamentally between general school populations [40; 41; 42; 43; 44; 48; 49] and those specifically targeting overweight/obese children [45; 47; 50; 51] or higher cardiovascular risk [46]. This population selection appeared intrinsically linked to intervention intensity, as targeted interventions consistently achieved larger effect sizes compared to population-based approaches that demonstrated smaller but significant improvements across large cohorts. The relationship between duration, population risk, and sample size revealed that longer studies with general populations [41; 42; 44] could achieve meaningful effects through sustained moderate-intensity approaches, while shorter studies required either high-intensity interventions in targeted populations [47; 50] or innovative delivery methods in large cohorts [48] to demonstrate significant between-group differences. Intervention intensity and family engagement strategies showed clear interdependent relationships with retention and outcome achievement. High-intensity interventions [47; 50] featuring 90-min sessions 4\(\times\)/week or weekly 1.5-h training plus intensive counseling achieved substantial improvements, while moderate-intensity approaches [41; 48] with brief daily activities or gamification strategies showed significant but smaller effects, and low-intensity interventions [49] with progressive activities plus general education demonstrated limited between-group effects. These intensity patterns were consistently reinforced by family engagement levels, where studies with strong family components achieved markedly lower dropout rates of 5.3% [48], 9% [50], and 9.2% [47], compared to 16.8-43% in studies with limited family involvement [40; 44; 49]. Successful family engagement strategies including family sessions [47], parent education [42], home-based components [43], and motivational interviewing [45] appeared to amplify intervention intensity effects, suggesting that family involvement may serve as both a retention mechanism and an intervention enhancement strategy that extends program reach beyond individual participants. Outcome measurement comprehensiveness and success patterns reflected the complex interplay between intervention scope, duration, and implementation quality. While all studies assessed anthropometric measures, specialized assessments including blood pressure (8 studies), lipids (7 studies), glucose (5 studies), fitness (6 studies), and dietary intake (4 studies) were more prevalent in longer, intensive interventions, suggesting that comprehensive programs warranted broader physiological monitoring.