["Family Process, Volume 65, Issue 2, June 2026. ", "\nABSTRACT\nHigh‐quality partnerships between families and schools can bring enormous benefits to the development, learning, and well‐being of children. Although past literature has frequently identified the parenting self‐efficacy element of parental self‐regulation as a key determinant of the strength of the home–school partnership, this knowledge base relies heavily on cross‐sectional studies. This paper follows on from an article in Family Process reporting the findings of a cluster randomized trial of an evidence‐based parenting program designed to promote parental self‐regulation, namely the seminar version of the Triple P—Positive Parenting Program. The trial found post‐intervention improvements in two domains of the home–school partnership, namely parent–teacher communication and parent school‐based involvement. Given that the home–school partnership was not a target of the intervention, the current study conducted a mechanism of change analysis to examine whether improvements in the home–school partnership could be attributed to post‐intervention improvements in parental self‐regulation. Data were collected from a sample of 912 parents of children attending 160 different primary schools across three Australian states. Following a Random Intercept Cross‐lagged Panel Model (RI‐CLPM) approach, bidirectional within‐participant effects between parental self‐regulation and parent–teacher communication were found, while unidirectional within‐participant effects were found for parent school‐based involvement. The findings provided support to the proposed theory of change where improvements in parental self‐regulation are the underlying mechanism behind reported post‐intervention improvements in the quality of the home–school partnership. The findings also support the potential spillover benefits of school‐based delivery of evidence‐based parenting programs.\nTrial Registration: Australian New Zealand Clinical Trials Registry: ACTRN12623000852651\n"]