A cluster randomized design was used to investigate effects of the Story Friends vocabulary curriculum on learning of 84 preschoolers in 24 classrooms who were at risk for language difficulties. Children in the treatment condition received explicit vocabulary instruction of 36 words during small-group storybook listening centers with extended practice opportunities in the classroom and at home. Children in the comparison condition were exposed to the same words in stories without explicit instruction or extended practice. Children (n = 16) with average or above language skills from six treatment classrooms were included to examine the impact of extended practice. Children at risk in treatment classrooms learned significantly more words (52%) than children at risk in comparison classrooms (12%). Children not at risk learned vocabulary equal to children at risk. A tiered approach to implementing Story Friends appears feasible for enhancing the vocabulary learning of preschoolers with and without language delays. [This is the online version of an article published in "Journal of Early Intervention."]