The aim of this article is to demonstrate how relational experiences with parents and preschool teachers provide children with a feeling of security that facilitates the development of competence in different domains. We first focus on the mechanisms regarding how secure attachments to parents serve as an important foundation for later development. We then provide a short review of the literature on teacher-child relationships, including results of our own research, which emphasizes the unique role relationship experiences with teachers play in shaping children's development. Teachers' sensitivity seems to be of particular importance in helping children with less favorable caregiving experiences at home to become engaged in corrective relational experiences, and there is evidence that interventions aimed at increasing teachers' sensitivity can be successful.