Despite evidence of the effectiveness of coaching as a form of ongoing professional development for educators, including in early childhood education, the field lacks an understanding of what the key components of coaching are and how and why they ‘work’. An improved theoretical basis for coaching would assist in identifying these underlying mechanisms of change. However, the field has been largely undertheorised, and an awareness of which theories have been applied in the field is lacking. This study entailed a meta-narrative review of the literature to identify which theories have informed the study of ongoing professional development in education, with a focus on coaching for early childhood educators. We identified 11 foundational papers addressing ongoing professional development in education that proposed or applied theories, and 69 papers on coaching for early childhood educators with a theoretical focus published between 2002 and 2022. Among both groups of papers, there were 47 different main theories applied or proposed. The findings indicate that coaching and other forms of ongoing professional development in education remain undertheorised and theoretical consensus is lacking. The findings suggest that further empirical testing of theories is required before any path towards building a theoretical consensus will become clearer.