Purpose The purpose of this paper is to outline the development, piloting and evaluation of the Who’s Challenging Who? (WCW) training intervention for social care staff to improve their empathy and attitudes towards people with learning disabilities (LD) and challenging behaviour (CB). Design/methodology/approach A phased approach was taken to the development and testing of the intervention. Initially, the existing literature was reviewed, the theoretical background of the intervention was developed, and then the intervention was designed. A pilot study was undertaken, followed by further development, and a large-scale randomised controlled trial (RCT). Findings WCW had a small positive effect on staff empathy 20 weeks after the intervention, and small to moderate effects for other staff reported outcomes (e.g. positive empowerment attitudes and positive work motivation). Being trained by people with LD and CB encouraged staff to reflect on the impact they have on the people they support. The trainers with LD valued their role, and saw benefits beyond this (e.g. friendships). Research limitations/implications It is possible to carry out high-quality RCT evaluations of social care practice, and research should continue to generate evidence in this way, as in healthcare settings. However, there were difficulties in retaining participants. Practical implications People with LD can be actively involved in the co-production and delivery of social care training. Social implications Employment and a fair wage can increase the confidence and empowerment of people with LD. Originality/value This is the first large-scale RCT of an intervention that aimed to improve empathy/change attitudes in social care staff who work with people with LD and CB.