Teachers' initial level of interactional quality at the beginning of a school year (baseline) was examined as a potential moderating factor in the relation between change in interactional quality and change in children's school readiness skills throughout an academic year. Participants were 269 preschool teachers and 1179 children from low-income backgrounds. Teacher-child interactions and children's school readiness skills were measured in the fall and spring of the preschool year. Overall, improvements in the quality of teacher-child interactions across the year were not significantly related to children's skill development. Three important findings emerged; two main effects and one interaction effect. Gains in teachers' instructional support across the year were related to children's literacy and inhibitory control development. Additionally, the relation between gains in teachers' emotional support and gains in children's inhibitory control was moderated by teachers' initial level of emotional support at the beginning of the year. (author abstract)