Background: Control-IQ (Tandem Diabetes) is a hybrid closed-loop (HCL) system that users self-initiate after completing online training. Best practices for clinical followup are not known. Our quality improvement objective was to evaluate the usefulness of an educator-led follow-up program for new HCL users in a type 1 diabetes pediatric clinic.Methods: We implemented an ''HCLCheck-in'' program, first determining when users started HCL, then having diabetes educators contact them for a follow-up call 2-weeks after start. Educators used a Clinical Tool to inform insulin dose and behavior recommendations, and used four benchmarks to determine need for further follow-up: ≥71% HCL use, ≥71% CGM use, ≥60% Time-in-Range (TIR, 70-180 mg/ dL), <5% below 70 mg/dL. Family and educator satisfaction were surveyed.Results: One-hundred-twenty-three youth [mean age 13.6 ± 3.7 y, 53.7% female, mean HbA1c 7.6 ± 1.4% (60 mmol/mol)] completed an HCLCheck-in call a median (IQR) of 18(15, 21) days post-HCL start. 74 users (60%) surpassed benchmarks with 94% HCL use and 71% TIR. Of the 49 who did not, 16 completed a second call, and improved median TIR 12.5% (p = 0.03). HCL users reported high satisfaction with the program overall [median 10 (9, 10) out of 10]. Educators spent a median of 45 (32,70) minutes per user and rated satisfaction with the program as 8 (7,9.5) and the Tool as 9 (9, 10). Conclusion:Our HCLCheck-in program received high satisfaction ratings and resulted in improved TIR for those initially not meeting benchmarks, suggesting users may benefit from early follow-up. Similar programs may be beneficial for other new technologies. K E Y W O R D S hybrid closed loop, pediatrics, program evaluation, quality improvement, type 1 diabetes 1 | INTRODUCTION Diabetes technology options have greatly increased for persons with type 1 diabetes (PWD) in the past decade, with the commercialization of multiple advanced insulin pumps, including hybrid closed-loop (HCL) systems. 1 HCL systems consist of an insulin pump, a connected continuous glucose monitor (CGM), and an algorithm to increase or decrease insulin delivery in response to glucose levels. The most recently available hybrid closed loop system, the t:slim X2 with Control-IQ technology (''Control-IQ'', Tandem Diabetes), was commercially approved in the United States in January 2020 for PWD ages 14 and over and has since been approved for PWD ages 6 and