This paper capitalizes on the addition of geocodes for Head Start centers in which children were randomly assigned to address questions about the role of neighborhood characteristics in moderating impacts of assignment to the Head Start program. Researchers explore the extent to which impacts of assignment to Head Start on outcomes for children vary by the availability of alternative child care options, as well as the presence of community crime and neighborhood socioeconomic disadvantage. This research uses data from the Head Start Impact Study and includes 4,440 3- and 4-year-old children who were randomly assigned off a waitlist in 351 Head Start programs across 81 Head Start grantees to either receive an invitation to participate in Head Start services, or to the control group (no offer of Head Start). Randomization was conducted based on 202 center groups: a total of 2,644 children were randomized to receive Head Start services and 1,796 were randomized to the control group. Ultimately, children enrolled in 1,632 classrooms across 930 Head Start and non-Head Start centers. Researchers matched center geocodes to data from the US Department of Education (DOE), the American Community Survey, and Economic Census data to assess availability of alternative child care and preschool options. Initial results demonstrate: (1) a significant effect of child care availability on the treatment impact on children's PPVT scores; (2) no statistically significant effects of neighborhood characteristics on Head Start impacts were found for children's Woodcock Johnson Letter Word Identification; and (3) neighborhood crime analyses reveal evidence for treatment moderation of Head Start's impact on children's PPVT scores. Figures are appended.