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.