To develop a text messaging intervention using MyDiaText and to determine whether such an intervention will decrease HbA1c in children 12 to 18 years old. The intervention will consist of daily text messages sent to the subject's personal mobile device. Previously developed text messages based on the American Diabetes Association (ADA) behavior goals will be used for this intervention. These will be adapted with input from the focus groups that will be carried out with adolescents with Type 1 diabetes mellitus (T1DM). The details of the intervention, such as frequency and timing of text messages, will be determined from input obtained from the focus groups.