This short-term longitudinal study examined how economically-impoverished children's moral reasoning predicts specific aggressive subtypes. Children (N = 106, M[subscript age] = 52.78 months, 51% boys, ethnically diverse backgrounds) from urban Head Start programs completed a structured story-interview pertaining to moral reasoning and judgement of accidental harm. Six months later, teachers reported children's aggressive forms and functions. Findings support that impoverished children in some ways follow similar patterns as more affluent children, yet diverge in important, ecologically-relevant ways. Use of psychological harm reasoning strategies corresponded with less reactive aggression, and use of rule adherence strategies corresponded with less physical-proactive aggression. Findings suggest that conventional reasoning and care-oriented reasoning may work as a buffer to reduce specific aggressive behaviors for impoverished preschool children.