["Child &Family Social Work, Volume 31, Issue 3, Page 1748-1760, August 2026. ", "\nABSTRACT\nEfforts to implement co‐parenting interventions are impacted by varying degrees of engagement and programme completion. The aim of this study was to analyse data from a service‐led evaluation of a perinatal intervention targeting co‐parenting (Family Foundations) to examine predictors of programme completion and reasons for non‐completion. Family Foundations was delivered in Melbourne, Australia between 2019 and 2021. Psychosocial factors (e.g., mental health symptoms and inter‐parental conflict) collected at intake and pre‐intervention from each caregiver were examined as predictors of programme completion. A content analysis was used to summarize qualitative data on reasons for non‐completion. Of the 343 families who commenced Family Foundations, 267 families (77.8%) completed all 10 sessions. The odds of programme completion were higher amongst parents who self‐referred; were older, educated, employed or first‐time parents; reported no past or current addiction concerns; reported family support; and received Family Foundations fully or partially via telehealth. Reasons for non‐completion included difficulties finding time, lack of interest and life stressors. Although Family Foundations had a higher completion rate than other multi‐session parent‐focused interventions, parents experiencing more psychosocial risk factors were less likely to complete the intervention. The findings from this study can inform the development and implementation of strategies to promote completion of Family Foundations among higher‐risk families.\n"]