This randomized controlled trial investigated the efficacy of Attachment and Biobehavioral Catch-up (ABC; Dozier, Bick, & Bernard, 2011) in reducing disrupted parenting behavior (affective communication errors, role/boundary confusion, fearful/disoriented, intrusive/negativity, and withdrawal) and its association with disorganized attachment. Participants were 105 mother–child dyads randomized to receive either ABC or a control intervention (a 10-session home-visiting intervention focused on improving children's cognitive abilities, gross and fine motor abilities, and language development). At the time of study enrollment, mothers were approximately 26.7 years old (SD = 7.8) and predominantly Black or African American (73.9%). At the first follow-up visit, children were approximately 20.7 months old (SD = 6.3) and most were identified as Black or African American (61.9%). Fifty-two percent of children were male (n = 55). Assessments of disrupted parenting behavior and child attachment quality were assessed approximately 7 months postintervention (SD = 5.8). A one-way analysis of variance revealed that parents who received ABC demonstrated lower levels of parental withdrawal than parents who received the control condition. A structural equation model revealed a significant indirect effect of intervention group on attachment quality through lower levels of parental withdrawal. Results add to the efficacy of the ABC intervention and identified parental withdrawal as a mediator of change.