Dante Cicchetti, the architect of developmental psychopathology, has influenced so many of us in profound ways. One of his many contributions was in demonstrating the power of randomized controlled trials (RCTs) to study the effects of Child–Parent Psychotherapy (CPP). These RCTs have shed light on causal mechanisms in development. Following Cicchetti and colleagues’ work, we designed a brief home visiting program, Attachment and Biobehavioral Catch-up (ABC), to help parents respond in sensitive, nurturing ways, so as to enhance children’s attachment and self-regulatory capabilities. In the current study, we assessed adolescents’ reports of the closeness of their relationships with their mothers 12 years after their mothers completed the intervention. A total of 142 adolescents participated (47 randomized to ABC, 45 randomized to a control intervention, and 50 from a low-risk comparison group). Adolescents whose mothers had been randomized to ABC reported closer relationships with their mothers than adolescents randomized to the control condition, with significant differences seen on approval, support, companionship, and emotional support subscales. Consistent with Cicchetti et al.’s work, these results provide powerful evidence of the long-term effects of an early parenting intervention.