One year after participating in the Research-based, Developmentally Informed (REDI) intervention or "usual practice" Head Start, the learning and behavioral outcomes of 356 children (17% Hispanic, 25% African American; 54% girls; M[subscript age] = 4.59 years at initial assessment) were assessed. In addition, their 202 kindergarten classrooms were evaluated on quality of teacher-student interactions, emphasis on reading instruction, and school-level student achievement. Hierarchical linear analyses revealed that the REDI intervention promoted kindergarten phonemic decoding skills, learning engagement, and competent social problem-solving skills, and reduced aggressive-disruptive behavior. Intervention effects on social competence and inattention were moderated by kindergarten context, with effects strongest when children entered schools with low student achievement. Implications are discussed for developmental models of school readiness and early educational programs.