<p>Improving the dietary quality of adolescents is crucial in public health, especially in low-income countries like Ethiopia. Despite numerous nutritional interventions, those interventions targeting adolescents were inconsistent due to fragmented implementation. Thus, this study aimed to evaluate the effect of selected double-duty interventions on the dietary diversity scores (DDS) of adolescents in Debre Berhan Regiopolitan City, Central Ethiopia. A two-arm parallel cluster randomized controlled study involved 708 adolescents (356 for intervention group (IG) and 352 for control group (CG)) was conducted from October 13, 2022 to June 30, 2023. The study found a 30.4% reduction in the proportion of adolescents with low DDS in the IG along with an 18.4% increase in high DDS compared to the CG as measured by the minimum dietary diversity score indicator. The generalized estimating equation (GEE) model revealed that adolescents in the IG were nearly twice as likely to achieve a high DDS compared to the CG [AOR = 1.91, 95% CI (1.85, 1.97)]. This study highlights the effectiveness of double-duty interventions supported by behavioral models in enhancing dietary diversity and advocates for their integration into nutritional policies.</p><p><Emphasis Type="BoldItalic">Clinical Trials:</Emphasis> The trial was prospectively registered at ClinicalTrials.gov (NCT05574842) and was first posted on October 12, 2022.</p>