This paper investigates the long-term impact of participation in the Chicago School Readiness Project (CSRP) during the Head Start year on children's behavioral outcomes at the end of their Kindergarten year. The primary questions addressed in the paper are: (1) What is the experimental impact of CSRP on two-year change (from Fall Head Start to the end of Kindergarten) in children's externalizing and internalizing outcomes, controlling for key baseline child, classroom and teacher covariates? (2) Building on recent findings from intervention studies that demonstrate significantly stronger impacts for families facing a greater versus smaller number of poverty-related risks, is the two-year impact of CSRP moderated by child-level baseline demographic covariates (including child gender, race/ethnic background, family socioeconomic risk, and community risk) and baseline levels of behavioral risk? (3) Addressing school factors that may account for enhanced for reduced intervention effects due to the transition to Kindergarten, is the two-year impact of CSRP moderated by school characteristics in Kindergarten? Overall 602 children and 94 teachers participated in the CSRP. Results after the Head Start year indicate significant treatment effects for teacher-reported and independent observations of children's internalizing and externalizing behavior problems, with effect sizes ranging from d = 0.53 to d = 0.89 (Raver et al., 2009). Moreover, there was some evidence for the moderating role of child gender, race/ethnic group membership, and exposure to poverty-related risk, with stronger effects of intervention for some groups of children than for others.