Early care and education programs have demonstrated strong impacts on the development and school readiness of young children, with particular benefit for children growing up in poverty. Within these programs, teacher-child interactions have been identified as they key active ingredient underlying the impacts on children’s development. However, limitations in conceptualization and measurement have hindered efforts to elucidate the most important features of teacher-child interactions and for whom and under what conditions these beneficial interactions occur and demonstrate impact. Guided by the Bioecological Model and Differential Susceptibility Theory, this dissertation first provides a conceptual framework to guide the examination of individual children’s experiences with teachers and associations between individual experiences and development in preschool. The second paper utilizes a person-centered analytic approach to assess how multiple developmental characteristics of children associate with their individual experiences with teachers. Membership in the profile with low developmental skills across domains was associated with teacher reports of more conflict and less closeness and higher levels of observed conflict between teachers and children. The third paper examines the association between children’s self-regulation and growth in academic skills and whether children’s individual experiences with teachers mediates this association. Results provided little support for mediation, but indicated links between children’s self-regulation and some aspects of experiences with teachers and academic growth.