This project was funded as part of an NHS England research programme to develop patient-centred outcome measures (PCOMs) for use with children and young people. Our aim was to develop a PCOM for NHS paediatric wheelchair and posture services. Over 60,000 children are registered with NHS wheelchair services in England, so identifying and addressing the outcomes of most importance to these users could help services to maximise the benefits achievable within available resources. None of the outcome measures currently in use among rehabilitation specialists are thought to meet fully the needs of wheelchair and posture service provision in the UK in identifying the outcomes of importance for children and young people. The project team comprised researchers from Bangor University’s Centre for Health Economics and Medicines Evaluation (CHEME), and staff from the Shropshire Wheelchair and Posture Service and the two Clinical Commissioning Groups (CCGs) that it serves. Additional input was gained from service users and parents/carers. A questionnaire survey was sent to young wheelchair users (<18 years) and their parents to explore the importance of a range of pre-defined outcomes and to identify novel outcomes. Subsequent face-to-face interviews were conducted to further explore survey responses and to uncover novel outcomes. Participants were also asked to score and record their satisfaction levels for the outcomes they identified as most important. Questionnaires were completed by 21 young wheelchair users or their parents, followed by 11 interviews. Based on the findings of the survey and interviews, and in consultation with the service providers and service users, the WATCh (Wheelchair outcomes Assessment Tool for Children) questionnaire tool was developed to allow clinicians and therapists to identify, score and monitor individual users’ most important outcomes before and after wheelchair provision. The WATCh tool was further refined through piloting in clinic. The final version comprises 16 outcome options, from which service users select their five most important outcomes to be monitored, describe what they wish to achieve, and rate their current satisfaction with each outcome. A follow-up WATCh tool has also been developed to allow monitoring of outcomes after wheelchair provision. The WATCh tool allows wheelchair users across a wide range of ages and clinical needs to select outcomes of most importance to them and to give an example of what they hope to achieve for each one. It allows a degree of comparability across patients, and ensures that patients focus on achievable outcomes. The simple before and after scoring system should allow service providers to ascertain how well desired outcomes are being achieved, both for individual users and for a specific outcome across service users. The tool should be applicable to children and young people accessing wheelchair services across the UK and other countries. In conclusion, the project achieved the aim of developing a novel, patient-centred outcome measure, the WATCh tool, which is suitable for use with children and young people accessing NHS wheelchair services. In addition to potentially improving the quality of service provided to young wheelchair users, the development of the WATCh tool could inform the development of novel PCOMs in other service areas.