Purpose: Approximately 50% of families who initiate a weight management programme (WMP) will not complete. It is fundamental to understand why participants initiate and complete a programme, and to ensure that programmes are effectively designed and delivered. This study examined the reasoning for family (young person and parent) engagement in three different and diverse WMPs. Methods: A multiple instrumental case study approach was employed. Three community-based WMPs participated: MoreLife, SHINE, and Weigh to Go. Clear design and implementation differences existed between WMPs. Multiple WMPs were recruited to examine the generalisability of research findings, and extract key features associated with participant engagement. Thirty families took part (~10 per programme). Data were collected early in the programme (0-2 weeks) and immediately after completion or dropout (within two weeks). Young people took part in a Participatory Action Research (PAR) session (interactive activities to generate meaningful information), and parents completed semi-structured interviews. A deductive line of inquiry was used; questions were based upon participant characteristics, environmental interactions, psychological processes and programme interactions. Interview data was transcribed verbatim and analysed alongside the PAR data using content and thematic analysis (themes presented in italics). Results: Preliminary findings indicate that families often engage in a WMP for non-weight related reasons. Such reasons include: management of mental health, to improve self -esteem, and to create friendships. Families remain in a WMP when: the programme suits their needs, they fit in amongst other participants, strong relationships are fostered with staff, and have strong support networks. Numerous families completing programmes prioritised WMP attendance above other leisure activities, and had plans in place to ensure they could attend each session. Low engagement was due to situational factors (e.g. logistic barriers [transport, timing…]) rather than programme dissatisfaction. Conclusions: Families attend community-based WMPs for reasons beyond weight management. Additionally, the families identified unique WMP features (e.g. maintenance programmes and non-clinical staff) which encourage programme attendance. Such features can be replicated in multiple, diverse settings. Understanding participant engagement is critical to designing and implementing efficacious WMPs
