Family members of people with eating disorders (EDs) have high levels of stress and can use maladaptive methods of coping. We have developed an intervention, using motivational interviewing (MI) strategies that trains lay and professional carer coaches (CCs) to support carers of adolescents with EDs to use more adaptive coping procedures. The aim of this study is to measure treatment integrity in coaches with either academic or lived experience. Eleven coaches were trained and supervised by an expert trainer and an ‘expert by experience’ trainer. Six of the coaches had prior training in clinical work and/or psychology and five had personal experience of supporting a loved one with an ED. Two audio-taped sessions (Sessions 3 and 7) from each family coached (n = 22) were assessed for fidelity to MI. Half the sessions (50% n = 11) had a Motivational Interviewing Treatment Integrity global score above the suggested cut-off for recommended competency. Prior clinical training was related to higher treatment fidelity and experiential training (having coached a greater number of families) improved treatment fidelity in the lay carer group. These preliminary findings suggest that: “lay CCs” can be trained to deliver an intervention based on MI. Further exploration of a more effective means of training, monitoring and supervision is required to maximise the quality of the intervention.