Personalized Digital Treatment for Adolescent Anxiety: A Feasibility Trial

The goal of this feasibility study is to test whether a new blended digital intervention for adolescents with anxiety disorders is feasible and acceptable for use, and to help plan future larger scale studies. The main questions it aims to answer are: * A: Can the investigators recruit appropriate participants? * B: How appropriate are the data collection procedures and outcome measures? * C: Are the study procedures and interventions suitable for and acceptable to the participants? * D: Does the research team have the resources and ability to manage the study and intervention? * E: Does the intervention show promise of being successful for adolescents with anxiety disorders? Participants will: * Receive outpatient anxiety treatment, typically every other week or weekly. * Use the Sidekick app as a homework supplement to plan, carry out, and evaluate exposure exercises between treatment sessions. * Complete questionnaires before, during, after, and three months after using the app. * Some participants and therapists will be invited to take part in qualitative interviews following the intervention.