BackgroundSocial prescribing is a mechanism of connecting patients with non-medical forms of support within the community and has been shown to improve mental health and wellbeing in adult populations. In the last few years, it has been used in child and youth settings with promising results. Currently, pathways are being developed for social prescribing in Child and Adolescent Mental Health Services (CAMHS) to support children and young people on treatment waiting lists. The Wellbeing While Waiting study will evaluate whether social prescribing benefits the mental health and wellbeing of children and young people.MethodsThis study utilises an observational, hybrid type II implementation-effectiveness design. Up to ten CAMHS who are developing social prescribing pathways as part of a programme run across England with support from the Social Prescribing Youth Network will participate. Outcomes for children and young people receiving social prescribing whilst on CAMHS waiting lists will be compared to a control group recruited prior to the pathway roll-out. Questionnaire data will be collected at baseline, 3 months and 6 months. Primary outcomes for children and young people are mental health symptoms (including anxiety, depression, stress, emotional and behavioural difficulties). Secondary outcomes include: loneliness, resilience, happiness, whether life is worthwhile, life satisfaction, and service use. An implementation strand using questionnaires and interviews will explore the acceptability, feasibility, and suitability of the pathway, potential mechanisms of action and their moderating effects on the outcomes of interest, as well as the perceived impact of social prescribing. Questionnaire data will be analysed mainly using difference-in-differences or controlled interrupted time series analysis. Interview data will be analysed using reflexive thematic analysis.DiscussionThe Wellbeing While Waiting study will provide the first rigorous evidence of the impact of social prescribing for children and young people on waiting lists for mental health treatment. Findings will help inform the prioritisation, commissioning, and running of social prescribing in other CAMHS. To maximise impact, findings will be available on the study website (https://sbbresearch.org) and disseminated via national and international networks.Trial RegistrationN/A.