This preregistered randomized controlled study investigated the effects of Video-Feedback Intervention to promote Positive Parenting and Sensitive Discipline (VIPP-SD) on parents' secure base script knowledge (SBSK). Furthermore, we examined whether effects of VIPP-SD on sensitive caregiving and sensitive discipline behavior and parents' attitudes toward these behaviors were moderated by SBSK at baseline. Families (n = 445) with pre- and school-aged children (n = 890) were randomized to receive VIPP-SD or telephone calls. Results showed no effects of VIPP-SD on SBSK. Furthermore, there was no moderation of effects on sensitive caregiving or sensitive discipline behavior by SBSK. VIPP-SD promoted positive attitudes toward sensitive caregiving and sensitive discipline behavior. The latter effect was moderated by SBSK: parents with lower SBSK showed the strongest improvements in positive attitudes toward sensitive discipline behavior. This effect was driven by a subgroup of younger children. These findings highlight the potential importance of tailoring interventions to meet the specific needs of parents with varying levels of SBSK.