Background: The transmission of attachment from parent to child is a well-known phenomenon. Previous research documented evidence supporting the transmission of attachment from parents to their children, with parental sensitivity serving a mediating role. Nevertheless, a "transmission gap" exists. Objective: In the current pre-registered study, we investigated whether parents' secure base script knowledge predicted their children's secure base script knowledge and whether this association was mediated by parental sensitivity and sensitive discipline. Furthermore, we examined whether these associations were moderated by the child's differential susceptibility. Method: We measured the Attachment Script Assessment (ASA) in parents at the second wave and in their 9-year-old children at the sixth wave, in one cohort (N = 239 families) of the longitudinal, six wave L-CID study. We observed parental sensitivity and sensitive discipline at the third wave. We used a polygenic score and child discomfort as differential susceptibility factors in the multilevel structural equation model investigating the intergenerational transmission of attachment. Results: Parental sensitivity, but not parental secure base script knowledge or parental sensitive discipline, predicted children's attachment. This association was moderated by child temperamental discomfort: lower levels of parental sensitivity predicted less secure child attachment in children with higher discomfort but not in children with lower discomfort. Conclusions: If replicated, we may conclude that the intergenerational transmission of secure base script knowledge is moderated by temperament in a way consistent with the diathesis-stress model.