The hypothesis was tested that the new open-group Norwegian day-care centers would more than traditionally organized centers negatively affect (a) current and (b) future teacher-child relationships, and (c) the developmental legacy of preschool problem behavior. The focus was on eight hundred and fifty 4-year-olds from 153 centers who were followed up in first grade. Results of this natural quasi-experiment revealed that children from open-group centers (a) experienced less teacher-child closeness in preschool and (b) more teacher-child conflict in first grade, and (c) that high levels of preschool problem behavior forecast especially high levels of future teacher-child conflict, but only for children from open-group centers. Results highlight the importance of spatial and social organization of day care and their translational implications.