Background: Caregivers of children with autism spectrum disorders (ASD) often experience difficulties in responding appropriately to the needs of those children, who typically express attachment in distinct and nonconventional ways. This highlights the need for an attachment-based approach targeted at caregivers of children with ASD. Circle of Security Parenting (COSP), an attachment-based parenting program, is designed to increase caregivers' sensitivity to children's attachment needs. The aim of this study was to provide verification of the effectiveness of COSP in mothers of children with ASD.

Methods: This study was a non-randomized controlled trial. Sixty mothers of children with ASD aged 4-12 were recruited. Twenty mothers received the COSP intervention, while 40 did not. The characteristics of children in the control group were matched with those of the intervention group. To evaluate the outcomes of the intervention, changes in parental self-efficacy and mental health were assessed using the Tool to Measure Parenting Self-Efficacy (TOPSE) and the General Health Questionnaire-30 (GHQ-30). The children's improvement in emotional and behavioral problems was assessed from the mothers' perspective using the Child Behavior Checklist (CBCL). Both groups completed the assessments in parallel. Evaluations were compared between baseline (T1) and 6-month follow-up (T2).

Results: Scores for self-efficacy and mental health of mothers and behavior of children were significantly improved from T1 to T2 in the intervention group, but not in the control group. Participants' mental health was markedly worsened in the control group.

Conclusion: This study demonstrated that the COSP program for mothers of children with ASD improved their parental self-efficacy and mental health, and reduced their subjective sense of difficulties related to their children's behaviors. Our findings support the effectiveness of the attachment-based program for mothers of children with ASD, providing the groundwork for further studies of the attachment-based intervention for children with ASD and their families. Future studies with larger samples and randomization are also needed for direct evaluation of the improvement of children's attachment security, and for exploration of the synergistic relationship between various family support strategies and COSP. Trial Registration This trial was registered with the University Hospital Medical Information Network Clinical Trial Registry (No. UMIN000039574).