This study examined the effects of an intensive shared book-reading intervention on the vocabulary development of preschool children who were at risk for vocabulary delay. The participants were 125 children, who the researchers stratified by classroom and randomly assigned to one of two shared book-reading conditions (i.e., the experimental, Words of Oral Reading and Language Development [WORLD] intervention; or typical practice). Results on researcher-developed measures showed statistically and practically significant effects for the WORLD intervention with no differential effects for children with higher versus lower entry level vocabulary knowledge. The researchers detected no statistically significant differences on standardized measures. Results suggest that a combination of instructional factors may be necessary to enhance the efficacy of shared book reading for children with early vocabulary difficulties. (Contains 4 tables and 2 figures.)