This study evaluates the relationships between aspects of Chilean teachers' explicit vocabulary instruction and students' vocabulary development in kindergarten. Classroom videotapes of whole-class instruction gathered during a randomized experimental evaluation of a coaching-based professional development program were analyzed. The amount of conceptual information about words made available during these discussions was the only significant predictor of students' end-of-kindergarten vocabulary, when controlling for the density and diversity of teachers' language and time spent in explicit vocabulary support, as well as child and teacher demographics. Each additional standard deviation of conceptual information about words provided predicted a 0.11 standard deviation increase in students' vocabulary outcomes. Practice and policy implications of these findings are discussed.