The project will develop and pilot test a personalized medicine mobile health emotion regulation application (the m-health KeepCalm app) that incorporates physiological stress measurement to support evidence-based practices for reducing challenging behavior in children with autism spectrum disorder (ASD). As much as 80% of children with ASD exhibit challenging behaviors that can have a devastating impact on personal and family well-being, contribute to teacher burnout and require frequent hospitalization. Evidence-based practices for reducing these behaviors emphasize uncovering triggers, yet parents and teachers often report that challenging behaviors surface without warning. Challenging behaviors caused by emotion dysregulation can be the most difficult to predict, as children with ASD often have difficulty communicating their distress before it results in challenging behavior. Exciting recent advances in digital technology now allow measurement of momentary emotion dysregulation, using physiological indices. The investigators' pilot data from four separate samples demonstrate that increased heart rate predicts onset of challenging behavior in children with ASD. In order to tailor the m-health KeepCalm app to end users and avoid potential barriers to its adoption, in Aim 1, the investigators will evaluate the acceptability, feasibility, and appropriateness of app, and the needs of educational teams in managing stress in children with ASD and challenging behaviors, by conducting interviews with teachers of children with ASD, parents of children with ASD and school administrators, and conducting structured in-class observations with teachers. Through the activities of Aim 2, the researchers will improve the m-health KeepCalm app, building on their initial app prototype, in collaboration with their established research partner, the Translational Informatics Unit, Children's Hospital of Philadelphia, and their established community partner, the School District of Philadelphia. The investigators will do this through 1) exploratory work on the specificity of heart rate increase to challenging behavior, on app clinical decision support timing, and on the association of app false positives and negatives to movement or child factors; 2) monthly advisory board meetings with expert stakeholders for app development guidance, and; 3) rapid-cycle prototyping of the app with 10 educational teams (i.e. 1-2 children with ASD, and their teacher and classroom aide, if they have one). This will allow for iterative improvement based on each user's experience. Through Aim 3, the researchers will test the app for usability, acceptability, feasibility and appropriateness, as well as preliminary effectiveness with 30 educational teams in a randomized waitlist field trial over a 3-month period. Successful completion of these aims will result in a novel m-health app designed to help teachers support emotion regulation, and reduce or prevent challenging behavior in children with ASD, using evidence-based strategies. These activities will lay the foundation for an R01 to evaluate the effectiveness of the m-health KeepCalm app in a full- scale randomized field trial. This proposal aligns with the strategic plan of the Interagency Autism Coordinating Committee, to maximize the potential for technology-based interventions to improve the lives of people with ASD.