Real-time Engagement for Learning to Effectively Control Type 2 Diabetes

The goal of this clinical trial is to learn if a new smartphone app that pairs glucose and exercise data will help adolescents and young adults with type 2 diabetes improve glycemic control. It will also study how changes in glycemic control are maintained over time. The main questions it aims to answer are: * Does using the app help with short-term glycemic control? * Does using the app help with longer-term glycemic control? * Does using the app help increase physical activity? Participants will: * Wear a continuous glucose monitoring device for 6 months * Wear a physical activity tracker for 6 months * Use the study smartphone app for 6 months * Complete 3 in-person study visits with fasting blood draws * Report dietary intake intermittently throughout the study

Inclusion Criteria: * type 2 diabetes: negative diabetes autoantibodies, no suspicion for monogenic diabetes * English-speaking (app in English) Exclusion Criteria: * Current pregnancy * Hydroxyurea use (CGM sensor inaccuracies) * Cognitive impairment or severe psychiatric condition that could interfere with participation in behavioral intervention for diabetes self-management * Current or previously diagnosed eating disorder