Deficits in behavioral and cognitive regulation are prevalent in children reared in poverty relative to more affluent children due to the effects of adverse conditions on the developmental underpinnings of these skills. Despite evidence to suggest that these emergent processes are susceptible to environmental inputs, research documenting short-term intervention program influences on these regulatory domains in young impoverished children is limited. We sought to determine the proximal effects of a universal school-based intervention (the PATHS Curriculum) on social, emotional, relational, and cognitive outcomes in urban poor kindergarten children. Four schools in high-poverty neighborhoods with similar demographic characteristics were randomly assigned to either PATHS or an attentional control. Teacher-reported measures of behavior (e.g., attention, concentration, aggression), peer nominations (e.g., likability, aggression, acceptance), and tasks gauging inhibitory control were administered in the fall of kindergarten and again in the spring after one academic year (about 6 months) of PATHS. Children who received PATHS exhibited significantly greater improvements than control students across all teacher-rated behavioral measures of social competence (i.e., emotion regulation, prosocial behavior, peer relations) and behavioral problems (i.e., aggression, internalizing behaviors, impulsivity and hyperactivity) at post-test as well as improvements in motor inhibition. This line of research constitutes an important frontier for prevention research given the implications for improving ultimate outcomes for otherwise disadvantaged children.