Prevention of Attachment Insecurity, Physiological Dysregulation, and Child Behavior Problems - A growing body of scientific evidence demonstrates that secure attachment and sensitive caregiving are important sources of resilience for children living in stressful environments (e.g., Graham & Easterbrooks, 2000), contributing to children’s mental and physical health (Shonkoff, 2016). Conversely, research indicates that insecure attachment is an important risk factor for the development of both childhood behavior problems and physiological dysregulation (e.g., Luijk et al., 2010; see Fearon et al., 2010, and Groh et al., 2012, for meta- analytic findings). Thus, efforts to prevent insecure attachment are crucial for children’s healthy development. Although a few promising approaches to preventing insecure attachment, physiological dysregulation, and childhood behavior problems have emerged (see Berlin et al., 2016), none has achieved widespread implementation. What is urgently needed is evaluation of a comprehensive theory- and research-based intervention protocol that can be widely implemented among families whose children are at elevated risk for developing or maintaining insecure attachments, physiological dysregulation, and behavior problems. The goal of the proposed study is to conduct an RCT of the Circle of Security – Parenting (COS-P) intervention within Early Head Start (EHS) programs, in light of evidence that EHS children and families are characterized by factors (e.g., low income, parental depression, exposure to violence/trauma; USDHHS, 2006a) that leave them at increased risk for insecure attachment and behavior problems. The project addresses the NICHD CDBB priority of promoting psychosocial adjustment for at-risk children and of understanding contributors to positive outcomes that can occur despite high-risk environments. Moreover, the project addresses a critical barrier to progress in the attempt to reduce the risk of negative outcomes among at-risk children by testing the efficacy of an intervention that was designed in collaboration with families and staff from the real-world contexts in which it will be implemented. Principal aims are to examine whether the addition of this brief attachment-based intervention to regular EHS services will (1) reduce child insecure attachment, physiological dysregulation, and behavior problems; and (2) promote sensitive parental responses to child distress. Additional aims are (3) to examine potential moderators of intervention effectiveness and (4) to test whether changes in parental response to child distress act as a mechanism of positive change. We have chosen HS/EHS as a strong service delivery mechanism because it is a widely available resource in many communities, with an infrastructure and a commitment to the mental health of children. The HS/EHS program has shown positive outcomes in some areas, yet evidence of reducing the risk of insecure attachment is lacking (Spieker et al., 2005). The approach we take is noteworthy in that we consider the broader public health context in which our attachment-oriented prevention protocol can be widely implemented. The RCT includes 249 parent-child dyads from the Harrisburg, PA and Lehigh Valley, PA EHS programs.