IMPORTANCE Exposure to adverse childhood experiences substantially increases the risk of chronic health problems. Originally designed to treat child conduct problems, parent management training programs have been shown to be effective in preventing children from being exposed to further adversity and supporting children's recovery from adversity; however, there are increasing concerns that a core component of these programs, the discipline strategy time-out, may be harmful for children with a history of exposure to adversity. OBJECTIVE To investigate the comparative benefits and potential harms to children exposed to adversity that are associated with parenting programs that include time-out. DESIGN, SETTING, AND PARTICIPANTSThis nonrandomized waiting list-controlled clinical study was conducted at a specialist clinic for the treatment of conduct problems in Sydney, Australia. The self-referred sample included children with conduct problems and their caregivers. Eligibility was confirmed through clinician-administered interviews. Data were collected between February 14, 2018, and February 1, 2021. INTERVENTIONS Caregivers participated in a 10-session, social learning-based parent management training program. Caregivers were provided with parenting strategies aimed at encouraging desired behaviors through effective reinforcement and managing misbehavior through consistent limit setting, including the use of time-outs. MAIN OUTCOMES AND MEASURES The primary outcome was the parent-reported Strengths and Difficulties Questionnaire score, and secondary outcomes included subscale scores from the clinician-administered Diagnostic Interview Schedule for Children, Adolescents, and Parents. Multiinformant measures of child adversity were collected using the parent-reported Adverse Life Experiences Scale and the clinician-rated Maltreatment Index. RESULTS A total of 205 children were included in analysis (156 in the full intervention and 49 in the control condition; 158 boys [77.1%]; mean [SD] age, 5.6 [1.8] years [range, 2-9 years]). Compared with children with low adversity exposure, children with high adversity exposure showed greater reductions in the Strengths and Difficulties Questionnaire score from baseline (mean difference, 3.46