• Severe hypoglycemia [ Time Frame: 26 weeks ] [ Designated as safety issue: Yes ]
• Percentage of sensors values in range (71 mg/dL to 180 mg/dL) [ Time Frame: 26 weeks ] [ Designated as safety issue: No ]
• Biochemical hypoglycemia (percentage of sensor values </= 70 mg/dL [ Time Frame: 26 weeks ] [ Designated as safety issue: No ]
• Measures of variability: mean amplitude of glycemic excursions (MAGE), SD, mean absolute rate of changes [ Time Frame: 26 weeks ] [ Designated as safety issue: No ]
• Parental quality of life measures [ Time Frame: 26 weeks ] [ Designated as safety issue: No ]

The purpose of this study is to determine the efficacy, tolerability, safety, and effect on quality of life of CGM in children 4 to less than 8 years of age with type 1 diabetes.

On the day of enrollment, a hemoglobin A1c level will be obtained, and potential subjects will be evaluated for study eligibility through the elicitation of a medical history and performance of a physical examination by a study investigator.

The subject will return for a second visit about 6 weeks after the enrollment visit. At this visit, quality of life questionnaires will be completed and a CGM sensor will be inserted. The monitor will be blinded so that the glucose values cannot be seen. The parent will be instructed on insertion, calibration, and care of the CGM.

The subject will return for a randomization visit 14 to 28 days after the blinded CGM was initiated.

• Subjects who have been compliant with use of the CGM and HGM will be randomized to one of two treatment groups: CGM Group or Control Group
• For the CGM Group, the CGM, HGM, and pump data (if applicable) will be reviewed and changes will be made to diabetes management as needed. Parents will be taught to use the protocol-developed instructions for changes to diabetes management to be used in real time based on CGM and HGM data. Instructions for downloading the CGM and HGM will be provided to subjects with a home computer.
• For the Control Group, a HGM and test strips will be provided. The HGM and pump data (if applicable) will be reviewed and changes will be made in diabetes management as needed. The blinded CGM data will be downloaded but will not be reviewed by study personnel until the end of the first 6 months of the study. Parents will be taught to use the protocol-developed instructions for how to make changes to diabetes management based on HGM data.

Both groups will have follow-up visits at 1,4,8,13,19, and 26 weeks (+/- 1 week) plus one contact between each visit (including one phone contact between the second visit and the one week visit) to review their diabetes management.

• Both groups will download device data on a weekly basis (if the subject has a computer). Subjects with email access will be instructed to email the downloaded data to the clinical center prior to each phone contact.
• For both groups, at each visit, the HGM and pump (if applicable) will be downloaded and for the CGM group, the CGM will be downloaded.

In the 13th and 26th weeks, the Control Group will use a blinded CGM for one week. The CGM Group will continue to use the blinded CGM. The Control Group will return the blinded CGM to the clinic after a week. The data will be reviewed by personnel who are not involved in the care of the subject to determine if additional blinded sensor data are needed. The blinded data will not be reviewed by the study personnel for management decisions until the end of the first 6 months of the study.

Following the 26-week visit:

• Subjects in the RT-CGM Group will continue to use the CGM.
• Subjects in the Control Group will be provided with a CGM and sensors after the week of blinded use and will have visits after 1 week and 4 weeks, with a phone contact during the first and second weeks.
• Both groups will have visits after 13 weeks and 26 weeks

• Active Comparator: Use of continuous glucose monitor for 12 months
• No Intervention: Standard glucose monitoring with a home glucose meter for 6 months, then use of a continuous glucose monitor for the second 6 months

Inclusion Criteria:

1. Clinical diagnosis of type 1 diabetes and using daily insulin therapy for at least twelve months
2. Age >4.0 to <10.0 years
3. HbA1c > 7.5%
4. Current insulin regimen involves either use of an insulin pump or multiple daily injections of insulin (at least 3 shots per day) for the last three months, with no plans to switch the modality of insulin administration during the next 6 months (e.g., injection user switching to a pump, pump user switching to injections, or the addition of Lantus (Glargine) insulin)

Exclusion Criteria:

1. Diabetes diagnosed <6 months of age
2. Use of a medication such as oral/inhaled glucocorticoids that in the judgment of the investigator will affect the wearing of the sensors or the completion of any aspect of the protocol.

3. The presence of any of the following diseases or another disease that the investigator believes to be a contraindication to participation in the protocol:

   • Asthma if treated with systemic or daily inhaled corticosteroids in the last 6 months (Intermittent treatment with inhaled corticosteroids does not exclude subjects from enrollment)
   • Cystic fibrosis (Celiac disease and adequately treated thyroid disease do not exclude subjects from enrollment)
4. Home use of CGM in past 6 months.
5. Participation in an intervention study (including psychological studies) in past 6 weeks.
6. Another member of the same household is participating in this study.