Background <p>While inactivity and sedentarism among adolescents are increasing globally, technology-based interventions incorporating wearable activity trackers (WATs) demonstrate the potential to combat the situation. With a focus on schools as critical environments in which to perform interventions among adolescents, this meta-analytic review of literature aimed to examine the effectiveness of wearable trackers in objectively measured physical activity (PA).</p> Methods <p>A systematic search was conducted across six databases—PubMed, CENTRAL, Scopus, SPORTDiscus, the Web of Science Core Collection, and PsycINFO—between January 2012 and March 2024. The language was restricted to English only. Both randomized controlled trials and quasi-experiment studies were included. Risk of bias was assessed using Cochrane RoB2 and ROBINS-I tools. Subgroup analyses and sensitivity analyses were performed. Effect direction for a narrative synthesis was also conducted. GRADE criteria were applied to assess quality of evidence.</p> Results <p>Fifteen studies were finally included in the literature review, and ten were adopted for meta-analysis. No statistical significance was found in intervention outcomes involving WATs’ effect on PA, whether in terms of total daily steps, moderate-to-vigorous PA (MVPA), or calorie counts. However, the subgroup analysis revealed that one study using research-grade assessment showed a substantial positive effect on steps. There were no data reported regarding the effect of objectively measured sedentary behavior.</p> Conclusion <p>Further study is needed to explore whether wearable activity trackers raise or decrease PA among adolescents in schools.</p> Registration <p>PROSPERO, registration number: CRD42023421008.</p>