This early efficacy study examined the effects of an automated storybook intervention designed to promote school readiness among at-risk prekindergarten children. Story Friends is a small-group intervention in which vocabulary and question-answering lessons are embedded in a series of storybooks. A randomized group design with an embedded single-case experimental design was used to examine treatment effects. Eighteen children from public prekindergarten programs serving families with low income were randomly assigned to the Story Friends treatment or a business-as-usual comparison. Participants in both groups completed measures of vocabulary and comprehension approximately monthly. Participants in the treatment group completed measures of instructional content for each book as part of the embedded single-case experimental design. Story Friends participants had significantly higher scores on measures of vocabulary than the comparison group and effect sizes were large, whereas more modest effects were shown for comprehension measures. Observations of treatment fidelity indicate that this intervention has the potential to be implemented with high fidelity in preschool classrooms. Results show a feasible means of teaching pre-K children challenging vocabulary that has the potential to facilitate later literacy development. (author abstract)