The impact of interactive storybook reading and embedded vocabulary instruction on expressive and receptive vocabulary learning of 4-year olds attending a Head Start program was evaluated. Ten tier two vocabulary words from two storybooks were targeted in a small group setting using repeated interactive storybook reading. The study examined whether explicit vocabulary intervention techniques provided within the interactive storybook reading increased word knowledge for preschool students from low socioeconomic households. Results comparing the treatment group with controls showed that both groups gained in receptive vocabulary knowledge, while a large effect-size was calculated for the intervention group. Semantic knowledge, or the ability to express the definitions of target words, showed small gains for the treatment group. Finally, the language sample data showed considerable spontaneous use of the target vocabulary words demonstrating expressive vocabulary skills. Keywords: vocabulary gap, language delay, Head Start, interactive storybook reading (ISR), explicit vocabulary intervention