Artificial Pancreas - Adolescent Physiology & Psychology Longitudinal Evaluation

The investigators will recruit adolescents with type 1 diabetes age 11-\<13 years and one parent to participate in this 24-month study. While this is admittedly a long enrollment time, study commitments following enrollment will be limited to three in-person or video visits at yearly intervals and one virtual or in-person device training session to improve adherence. Participants must be pubertal, as puberty appears to contribute significantly to the insulin resistance that is likely related to worsened blood glucose control. Pubertal assessments will occur at yearly intervals.

The first of the two arms/substudies ("Randomized" substudy) is a longitudinal randomized controlled trial for which participants will be randomized to either continue their current diabetes therapy (with the addition of use of a Dexcom CGM, forming the "Usual Care+CGM" Control Group; this includes both adolescents using non-automated insulin delivery (AID) insulin pumps or multiple daily injections \[MDI\]). The Experimental Group will use an AP system (Tandem's Control-IQ system) during the two-year duration of the study. The primary outcome of the Randomized substudy will be HbA1c between intervention groups at the 24-month visit.

The second arm/substudy ("Triple Label Surveillance" substudy) is an observational study. Both arms/substudies perform a "Triple Label" mixed meal study assessing glucose flux and insulin resistance that requires visits to the Clinical Research Unit. All participants will undergo a Triple-Labeled Glucose Assessment at months 0, 12 and 24. This assessment evaluates the degree of insulin resistance including in the hepatic and peripheral compartments. During Visit 2, all participants (for both the Triple Label sub-study and the Glycemia-Only sub-study) will complete multiple questionnaires assessing aspects of adolescent psychology and sociology. HbA1c will also be collected using a local lab. The primary outcome of the study overall (combined Triple Label Surveillance and Randomized substudies) is the change in insulin resistance between baseline and the 24-month visit.

CGM glucose data will be collected continuously via remote connection during the entire study. At months 6 and 18, participants will be contacted to obtain insulin management information and will have HbA1c measures assessed at a local clinic or laboratory. Additional scheduled phone calls will occur in the month before the in-person study visits to request HbA1c and confirm body composition/Triple-Labeled Glucose Assessment scheduling and discuss use of CGM and activity tracker. Participants will be contacted in the event of insufficient CGM or AP system use. For the Randomized substudy, in the Eperimental Group, insufficient use is defined as \<60% AP use over a 3-month period. For the Control Group, less than 1 month of CGM data over a 3-month period is considered insufficient. If participants do not meet minimum use criteria in 2 successive periods, the participant will be discontinued from the study.