This study revisits the premature autonomy model by examining parents’ use of positive behavior support (PBS) practices on a daily timescale to better understand underlying processes in developmental changes in family disengagement and the implications for adolescent problem behavior and substance use. This study included 151 9th and 10th grade adolescents (61.5% female) and their caregivers, who participated in a baseline assessment, a 21-day daily diary burst, and a 1-year follow-up assessment. Four key findings emerged: (a) on days when parents used more PBS, adolescents felt more close and connected to their caregivers; (b) adolescents who exhibited a larger-magnitude of change in connectedness with caregivers in relation to variation in positive parenting (termed fragile connectedness) were at higher risk for antisocial behavior, deviant peer involvement, and substance use one year later; (c) individual differences in initial levels of antisocial behavior and effortful control accounted for between-person variation in fragile connectedness; and (d) day-level adolescent anger and parent–adolescent conflict predicted within-family variation in parents’ use of PBS. Implications for the premature autonomy model and intervention science are discussed.