Background: As part of a study considering the impact of a child weight management programme when rolled out at scale following an RCT, this qualitative study focused on acceptability and implementation for providers and for families taking part. Methods. Participants were selected on the basis of a maximum variation sample providing a range of experiences and social contexts. Qualitative interviews were conducted with 29 professionals who commissioned or delivered the programme, and 64 individuals from 23 families in 3 English regions. Topic guides were used as a tool rather than a rule, enabling participants to construct a narrative about their experiences. Transcripts were analysed using framework analysis. Results: Practical problems such as transport, work schedules and competing demands on family time were common barriers to participation. Delivery partners often put considerable efforts into recruiting, retaining and motivating families, which increased uptake but also increased cost. Parents and providers valued skilled delivery staff. Some providers made adaptations to meet local social and cultural needs. Both providers and parents expressed concerns about long term outcomes, and how this was compromised by an obesogenic environment. Concerns about funding together with barriers to uptake and engagement could translate into barriers to commissioning. Where these barriers were not experienced, commissioners were enthusiastic about continuing the programme. Conclusions: Most families felt that they had gained something from the programme, but few felt that it had 'worked' for them. The demands on families including time and emotional work were experienced as difficult. For commissioners, an RCT with positive results was an important driver, but family barriers, alongside concerns about recruitment and retention, a desire for local adaptability with qualified motivated staff, and funding changes discouraged some from planning to use the intervention in future.