Immediate Effects and Experiences of a Digital Single-Session Behavioural Activation Based Intervention for Adolescents: A Single Arm Pre-post Programme Evaluation of Project ABC in the UK

Background: Self-guided Digital Mental Health Interventions (DMHIs) are increasingly used amongst young people as they are scalable and may improve access to support. Objective: To assess the acceptability, feasibility, utility, and immediate effects of Project ABC-UK, a Single-Session Behavioural Activation DMHI for UK youth. Methods: A single group pre-post design was used. Participants (aged 13–18) completed demographics, as well as measures of hope, self-agency, hopelessness, and perceived control before and after the online intervention. It was completed anonymously, and participants gave feedback. T- and chi-square tests compared completers and non-completers; pre-post effects were assessed using paired t-tests with effect sizes (Cohen’s d). Thematic analysis explored feedback. Results: Of 799 participants, 401 (50.1%) completed the intervention, of whom 356 (88%) completed at least one post-intervention measure. Completers were more likely to be younger, have higher pre-intervention hope and self-agency, and to identify as sexual minorities. Significant improvements were found in hope and self-agency (d = −0.41), hopelessness (d = 0.52), and perceived control (d = 0.45). Most found the intervention enjoyable and useful. Conclusion: Findings support the feasibility and acceptability of Project ABC-UK, with promising immediate effects on all outcomes. Future studies should assess effects on depression and anxiety at follow-up and compared to other interventions.