Introduction: Children with moderate to severe speech sound disorder (SSD) need intensive therapy to increase intervention effectiveness and efficiency. However, worldwide speech and language therapists (SLTs) report that it is difficult to implement recommended intervention intensities in clinical practice. Supporting parents/carers to deliver home-intervention, facilitated through digital tools, has the potential to circumvent these difficulties and increase practice intensity. This realist evaluation builds on our earlier realist review on intensive, digital, parent-implemented interventions for children with SSD through exploring the experiences of stakeholders to optimally understand what might work best, for whom, and why in clinical practice. Methods: We undertook a realist evaluation to test and refine our initial programme theories developed in our earlier realist review through focus groups with key stakeholders. Five focus groups were conducted with SLTs (n = 22), and two focus groups with parents/carers of children with SSD aged 4-5 years (n = 6). A realist methodology approach was used to collect and analyse the data, including the development of context-mechanism-outcome configurations. Middle-range theories of adult-learning, self-efficacy and parenting styles were used to develop our theoretical thinking. Results: Programme theories from the earlier realist review about how the intervention works were refined, refuted, or confirmed. The refined theories are presented across three areas to demonstrate the journey of engaging in a digital, intensive parent-implemented intervention: (1) Readiness to engage; (2) Implementation of the intervention; and (3) Sustaining momentum. The theories offer insight into mechanisms that support and train families to engage in home-practice through digital tools, including important contextual factors needing consideration in implementation. Conclusion: Digital, intensive, parent-implemented interventions for children with SSD have the potential to improve the effectiveness and efficiency of SLT services in certain contexts and improve children's outcomes worldwide. Mechanisms of change, and impactful contexts at each point of the journey of involvement need consideration to successfully empower and support parents/carers and their children with SSD.