In this study, we examined 1) whether a reading aloud intervention, Universidade do Bebê (UBB), had impacts on self-regulation, 2) whether effects on child outcomes were mediated by self-regulation, and 3) whether effects of UBB were explained through a sequential pathway of impact including cognitive stimulation in the home, parent-child interactive reading, and self-regulation. Method: We performed a cluster-randomized controlled trial of UBB in childcare centers serving low-income 2-4 year-old children in Northern Brazil. The childcare centers were randomized to receive UBB or standard care (control). Families in UBB could borrow children’s books weekly and participate in monthly workshops focused on reading aloud. Parent-child dyads (n=484, intervention=232, control=252) were evaluated at baseline and nine months later on: child self-regulation, vocabulary, IQ, working memory, and phonological memory; and measures of cognitive stimulation in the home and parent-child interactive reading. Results: The UBB group showed significant higher self-regulation (Cohen’s d=.25), compared to the control group, particularly in the subdomains of Attention (d=.24) and Impulse Control (d=.21). Previously shown impacts of UBB on receptive vocabulary, IQ, and working memory were mediated by self-regulation. Effects of UBB on self-regulation and child outcomes were partially explained through cognitive stimulation in the home and parent-child interactive reading. Conclusion: Selfregulation represents an important mechanism by which reading aloud interventions impact language and cognitive outcomes. Investigators should consider the role of self-regulation when refining interventions seeking to prevent poverty-related disparities.