Although an abundant literature documents preliterate children's word learning success from shared storybook reading, a full synthesis of the factors which moderate these word learning effects has been largely neglected. This meta-analysis included 38 studies with 2,455 children, reflecting 110 effect sizes, investigating how reading styles, story repetitions, tokens and related factors moderate children's word comprehension, while adjusting for the number of target words. Dialogic reading styles, tokens, and the number of words tested all moderated word learning effects. Children's age, who read the story, and time between story and test were not moderators. We identify story repetition and word types as topics which merit further research. These results provide information to guide researchers and educators alike to the factors with the greatest impact on improving word learning from shared storybook reading.