Diabetes mellitus is a growing public health concern in Johannesburg, South Africa, with high morbidity rates. A mixed-methods approach involving surveys and medical record reviews was employed to assess programme impact over a two-year period. Among participants in the intervention group, there was an observed reduction in HbA1c levels by 5% (95% CI: -6.3%, -2.8%), indicating improved glycemic control. The preventive care programmes significantly contributed to better diabetes management outcomes. Continued support and expansion of these programmes are recommended for further impact. Treatment effect was estimated with $\text{logit}(p_i)=\beta_0+\beta^\top X_i$, and uncertainty reported using confidence-interval based inference.