Purpose: This systematic review aimed to identify studies evaluating the impact of high-intensity interval training when delivered in school and sports training. Methods: A systematic search of 10 databases (September 2019) identified 24 eligible studies (including children and/or adolescents 5–18 years and reporting cardiometabolic health and/or health-related fitness outcomes), assessed for quality using the Cochrane Risk of Bias Tool (version 2.0). Outcomes were synthesized using a random-effects meta-analysis, and potential moderators were explored (i.e., study duration, risk of bias, age, and deliverer/instructor). Results: Standardized mean difference for the effects of high-intensity interval training were significant for body mass index g = −0.27 (p < .001), cardiorespiratory fitness g = 0.27 (p < .001), lower body muscular fitness g = 0.49 (p = .005), and upper body muscular fitness g = 0.37 (p = .002); but not for blood pressure (p > .05). Risk of bias results were variable (low = 8, some concerns = 9, and high = 7). Conclusion: Our findings suggest that embedding high-intensity interval training in schools and sports training can facilitate improvements in some aspects of cardiometabolic health and fitness in children and adolescents.