Education on insulin self-injection techniques is important for good glycemic control, but its effectiveness in some elderly patients is limited due to loss of cognitive function and impaired activities of daily living. We hypothesized that classification using the Dementia Assessment Sheet for Community-based Integrated Care System 8-items (DASC-8) would help identify elderly patients with diabetes who effectively learn self-injection techniques. Diabetes patients aged ≥ 65years who used a self-injection insulin pen were administered the DASC-8 and a questionnaire to evaluate insulin self-injection techniques, and then received technical education. The questionnaire was administered again 4months later, and patients were classified into the education-effective and education-ineffective groups. The achievement of HbA1c targets defined for each patient according to guidelines based on DASC-8 category was examined over 12months. 76 Japanese patients (median age 72.0years and 53.9% female) with DASC-8 categories I (n = 55), II (n = 13), and III (n = 8) were enrolled. In the education-effective group, the percentage of patients in category I was significantly higher than that of patients in category II or III (92.0% to 23.8%, P < 0.001). Category I was independently associated with education effectiveness (odds ratio 14.50, 95% confidence interval: 2.110-100.0, P = 0.007). Category I patients in the education-effective group showed significantly improved achievement of target HbA1c from baseline to the 12th month (from 27.6% to 62.1%, P = 0.008). The DASC-8 was a useful indicator for identifying elderly patients who would benefit from education on self-injection techniques. The online version contains supplementary material available at 10.1007/s13340-024-00710-z.