Purpose: Adolescence is a sensitive period for developing mental health problems. Interventions targeting emotion regulation have shown promising transdiagnostic effects for this group, but optimization efforts are called for. In the current study, we used an element-based approach to identify potentially active ingredients in interventions measuring emotion regulation, to guide further optimization. Methods: We coded practice elements in 30 studies based on a systematic review of mental health interventions measuring emotion regulation in adolescents (N = 2,389 participants, mean age 13-17 years). Using a three-level modeling approach, we then investigated the difference in effect on emotion regulation between studies of interventions with and without these practice elements. Results: We identified 75 practice elements and 15 element categories used in the included interventions. Results showed significantly stronger effects on emotion regulation when interventions included the practice elements Setting goals for treatment (difference in d = 0.40, 95% CI [0.09, 0.70], p = 0.012) and Psychoeducation about acceptance (difference in d = 0.58, 95% CI [0.09, 1.07], p = 0.021). Furthermore, a total of 11 elements and four overall categories were identified as potentially active ingredients, based on an effect size difference of > 0.20 between interventions with and without the elements. Conclusion: The results can direct experimental research into the selection of practices that are most likely key to mechanisms of change in interventions addressing emotion regulation for adolescents. The challenge of measuring emotion regulation is discussed.