We examine the roles of neighborhood characteristics in the development of the aggressive behavior of 1,409 urban boys and girls between the first and seventh grades. The multilevel, longitudinal growth analyses find strong neighborhood effects in all models, while controlling for individual-level variables. Results indicated that the effects of neighborhood violence, employment, income, and percentages of single males and female-headed households do not manifest in first grade, but affect the trajectory of child aggression between first and seventh grades. The influence of family income and frequent physical discipline on boys' and girls' aggression occurs at first grade, and family income has a modest effect on the trajectory. The findings strongly suggest that the neighborhood sources of the development of child aggression are independent and different from early childhood experiences. © 2010 Wiley Periodicals, Inc.