This study evaluates the effects of a coaching-based teacher professional development program on Chilean kindergarten teachers' explicit vocabulary instruction. Classroom videotapes gathered during the cluster-randomized evaluation of the Un Buen Comienzo (UBC) program were analyzed to identify the intervention impacts of training. The offer of training increased the probability that literacy instruction would occur by 26 percent and that vocabulary support would be provided during literacy by 25 percent. Controlling for the presence of literacy instruction, training increased literacy instruction by 13.68 min and increased vocabulary support during literacy by 2.87 min. However, training reduced the probability that other-topic instruction would occur by 25 percent and the probability of vocabulary support during other topics by 39 percent. Implications for the scope and focus of language-based teacher professional development are discussed. (author abstract)