Arriving late for scheduled contraceptive reinjections is common in many countries and contributes to discontinuation when providers are unsure how to manage such clients. A clinic-randomized cohort and cross-sectional study with more than 5,000 clients using injectable contraceptives was conducted in the Eastern Cape province of South Africa to test the effectiveness of a provider job aid for managing late-returning clients and promoting continued use of the method. A marginally significant difference in reinjection rates between intervention and control groups was found for those up to two weeks late, and reanalysis excluding one clinic that experienced stockout issues revealed a significant difference. The difference in reinjection rates for those 2–12 weeks late was also found to be significant. The one-reinjection cycle continuation rate for the intervention group was higher than that for the control group, but the difference was not statistically significant. Appropriate management of late-returning clients is critical, and this study illustrates that reinjection rates can be significantly increased with a low-resource provider job aid.