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.

We assessed impacts on classroom quality and on 5 child language and behavioral outcomes of a 2-year teacher professional-development program for publicly funded prekindergarten and kindergarten in Chile. This cluster-randomized trial included 64 schools (child N 1,876). The program incorporated workshops and in-classroom coaching. We found moderate to large positive impacts on observed emotional and instructional support as well as classroom organization in prekindergarten classrooms after 1 year of the program. After 2 years of the program, moderate positive impacts were observed on emotional support and classroom organization. No significant program impacts on child outcomes were detected at posttest (1 marginal effect, an increase in a composite of self-regulation and low problem behaviors, was observed). Professional development for preschool teachers in Chile can improve classroom quality. More intensive curricular approaches are needed for these improvements to translate into effects on children.