Objectives: Self-management education (SME) is recognized globally as a tool that enables patients to achieve optimal glucose control. While factors influencing the effectiveness of self-management interventions have been studied extensively, the impact of program length on clinical endpoints of patients diagnosed with diabetes is underdeveloped. This paper synthesized information from the existing literature to understand the effect of program length on glycated hemoglobin (HbA1C) in adults with type 2 diabetes mellitus. Methods: We searched Web of Science, PubMed, Scopus, MEDLINE, EMBASE, PsychINFO, and the Cochrane Central Register of Controlled Trials to identify relevant English language publications on diabetes self-management education published between January 2000 and April 2019. Results: The review included 25 randomized controlled trials, with 64.0% reporting significant changes in HbA1C. The studies classified as long-term (lasting one year and above) were associated with the greatest number of interventions achieving statistically significant (87.5% significant vs. 12.5% non-significant) differences in changes in HbA1C between the intervention and the control subjects, recording an overall between-group HbA1C mean difference of 0.6±0.3% (range = 0.2–1.2). Conclusions: Our findings suggest that program length may change the effectiveness of educational interventions. Achieving sustained improvements in patients' HbA1C levels will require long-term, ongoing SME, and support.