This study used a novel method to examine the volume and quality of teacher-child conversations within 44 preschool classrooms. Small group play sessions were transcribed, parsed into conversations, and coded for teachers' use of strategies that elicited and extended child talk. The first research aim was to examine the extent to which professional development impacted teachers' strategy use during conversations with children, whereas the second aim was to consider the way in which teachers' strategy use related to gains in children's vocabulary across the preschool year. Regarding this second aim, of principal interest was the relation between the pattern of teachers' strategy use (concentrated versus distributed) and children's gains. Findings indicated that professional development increased teacher-child engagement in multi-turn conversations, child-initiated conversations, and teachers' strategy use. In addition, teacher-child conversations with a high concentration of teacher elicitations and extensions were positively associated with children's vocabulary gains. This study increases our understanding of what teacher-child conversations look like in preschool settings, and helps to advance the field in terms of identifying features of conversations that may promote children's language growth. (author abstract)