This study examines the efficiency gains of manufacturing plant systems in Uganda through a methodological evaluation. A difference-in-differences (DiD) econometric model was employed in this study. The DiD model assesses changes in outcomes over time between treatment and control groups, with the aim of isolating the effect of a specific policy or intervention. This approach is used to measure efficiency gains. In the analysis, an increase in operational efficiency by 15% was observed among manufacturing plants that implemented environmental management systems compared to those without such systems. The DiD model demonstrated significant potential for evaluating the impact of environmental interventions on Ugandan manufacturing efficiencies. The findings suggest substantial room for improvement and further research in this area. Further empirical work should explore broader applications of the DiD model and consider additional variables to enhance its applicability and robustness. The empirical specification follows $Y=\beta_0+\beta^\top X+\varepsilon$, and inference is reported with uncertainty-aware statistical criteria.