The Lighthouse Parenting Programme (LPP) is a multifamily mentalization-based intervention for parents with child protection service involvement. The Supporting Parents Project was a randomized controlled trial of the LPP being delivered by children’s social care services. In this paper, the research and clinical leads of the project present some of their early findings and thinking in relation to parental mentalizing in this context. Early findings from the study showed unexpected results in relation to the assessment of parental reflective functioning. Issues around the measurement of parental mentalizing, and particularly pre-mentalizing modes, are discussed. We argue that learning from clinicians with experience of supporting parents through a mentalization-based approach can help researchers become more nuanced in their assessments. In the second half of the paper, we present some of the metaphors and imagery used in the LPP that has proven useful in helping parents and frontline practitioners to establish epistemic trust and methods for enhancing parental mentalizing.