The purpose of this case study is to offer reflections on the personal experiences, processes of behavioral change; and subsequent outcomes of designing and implementing a collaborative exercise psychology intervention. The intervention, based on Bandura’s (1977) Self Efficacy Theory and using self-efficacy related behavior change techniques (Michie et al., 2015), aimed to provide families affected by health inequalities with opportunities to enhance their understanding of health and make positive behavioral changes. This case is based around one female client aged 48 years of age who took part in the project with her ten-year-old daughter. Pre-intervention the client was engaging in minimal levels of weekly physical activity and reported poor self-rated mental well-being. Through improvements in self-efficacy, achieved through opportunities on the project, the client was able to make notable improvements to her physical activity levels leading to significant weight loss and improvements in mental well-being. From the practitioners’ perspective, reflection on areas for future work within the field of exercise psychology, particularly guidance on developing effective client-practitioner relationships with ‘hard-to-reach’ individuals and groups is warranted. More consideration for the suitability of the PA guidelines for individuals with poor physical and mental health is also required.