The Circle of Security–Parenting Intervention (COS-P; Cooper et al., 2009) is a psychoeducational program for caregivers of young children that has been widely disseminated. The program is founded in attachment theory and relies on computer-delivered content and parent reflection and discussion to teach concepts of safety and security to promote better caregiver-child relationships and child wellbeing. The present study is a randomized controlled trial of COS-P, individually delivered to 85 Australian caregivers (51 COS-P, 34 waitlist control) who reported parenting distress and child disruptive behaviors. Caregivers completed a baseline assessment and repeated the assessment after completion of COS-P or 8 weeks on the waitlist. Caregivers completed surveys to report child symptoms, and parenting stress, anxious and avoidant attachment, reflective functioning, parenting practices, and depressive symptoms. No differences in COS-P vs. waitlist participants were found at baseline. Analyses of complete data (35 COS-P, 25-26 waitlist) revealed a greater decline in caregivers’ attachment anxiety and negative parenting relative to waitlist, but only attachment anxiety in intent-to-treat analyses. Other improvements were found, but these extended to both the COS-P and waitlist conditions and did not differ between conditions. Overall, effects of COS-P were small and rarely significant, suggesting the need to consider alternative programs that have evidence of effectiveness when providing services to at-risk families.