Including parents of children with developmental delays in early intervention programs has been widely endorsed as best practice across the multiple disciplines that work in that context. Parents have echoed that sentiment, commenting on the benefits of being able to apply skills in broader family and community contexts. Despite a 20-plus year history of research showing the benefits of family-centred interventions, the skills required to successfully transition from therapist-lead to family-centred practice appear to have occurred through experience or chance. Systematic development of therapists' skills including through education, mentoring and reflective supervision have been promoted as being essential to facilitating the transition. This qualitative study investigated the learning experiences of 14 allied health professionals from various disciplines as they engaged in a relationally based, family-centred model, the Parent Child Relationally Informed -- Early Intervention (PCRI-EI) program. Feedback indicated the systematic approach embedded in the treatment manual combined with reflective supervision built therapists' competence and confidence in working relationally. They reported being able to use these skills to develop therapeutically sound, family-centred partnerships with parents as well as to promote socioemotional connection for the parent and child. These findings are discussed in the context of the successful implementation of best-practice early intervention programmes.