Adolescents and young adults with T1D and poor glycemic control (age 14-< 25 years, T1D duration >12 months, HbA1c 7.5-<11.0%, using an insulin pump or MDI)) will be randomly assigned to either CGM or BGM. Sample size will be 150. The primary outcome assessment will be HbA1c after 6 months. Secondary outcomes will include HbA1c, CGM metrics (control group will wear blinded CGM at 13 and 24 weeks), and quality of life measures. The randomized trial will be followed by a 6-month extension study during which the RCT control group will initiate CGM and the RCT CGM group will continue CGM.

Inclusion Criteria:

1. Clinical diagnosis of T1D, with either age of T1D diagnosis < 10 years of age OR a history of positive T1D related antibodies in the medical record
2. Age 14-<25 years
3. Diabetes duration ≥ 1 year
4. Total daily insulin requirement ≥ 0.4 units/kg/day
5. HbA1c 7.5% to <11.0% (Point of care device or local lab measured as part of study at screening visit)
6. Insulin regimen involves a consistent modality of insulin administration with either use of an insulin pump or at least 3 multiple daily injections of basal and bolus (meal time) analogue insulin. Insulin pump must not have been started within 3 months of consent with no plans to change regimens in the next 6 months
7. Perform at least 2 blood glucose meter checks per day from self-report at screening and an average of at least 2 checks per day from meter download during blinded CGM run in
8. Blinded CGM must be used a minimum of 200 hours (equivalent to 8.3 days) with an average of 1.8 calibrations per day during the blinded CGM screening period.
9. Participant comprehends written and spoken English
10. Participant understands the study protocol and agrees to it (if applicable)

Exclusion Criteria:

1. Use of unblinded personal CGM and/or flash CGM, outside of a research study, as part of real-time diabetes management in the last 3 months

2. Unable to use CGM device for minimum number of hours during blinded pre-randomization period or skin reaction from adhesive that would preclude participation in the randomized trial

3. Started on non-insulin medication for blood glucose control within the past 3 months or plans to begin within the next 6 months

4. The presence of a significant medical disorder that in the judgment of the investigator will affect the wearing of the sensors (such as a skin condition), or the completion of any aspect of the protocol.

5. More than 1 episode of DKA in the past 6 months as defined in the adverse events chapter.

6. The presence of any of the following diseases:

   • Asthma or any condition present in the last 6 months where treatment is a systemic or daily inhaled corticosteroid (Intermittent treatment with inhaled corticosteroids does not exclude subjects from enrollment)
   • Cystic fibrosis
   • Addison's disease (Adequately treated thyroid disease and celiac disease do not exclude subjects from enrollment)

7. Inpatient psychiatric treatment in the past 6 months or daily intensive outpatient psychiatric day treatment in the past 3 months.

8. Pregnant (positive test confirmed at screening) or planning to become pregnant in the next 12 months.

9. Need for use of acetaminophen or acetaminophen-containing products on a regular basis during the 6 months of the trial

10. Participation in a diabetes related intervention study in the past 6 weeks.

11. Any medical, psychological or social situation where per investigator discretion it may be difficult for participant to participate fully in the intervention

12. Any condition, per investigator assessment, that could impact reliability of the A1C measurement, such as (but not limited to) hemoglobinopathy, hemolytic anemia, chronic liver disease; chronic GI blood loss, red blood cell transfusion or erythropoietin administration within 3 months prior to screening