Based on its coincidence with a significant period in language development for children, preschool provides a favorable setting to foster vocabulary growth. The purpose of this study was to evaluate the effectiveness of two instructional conditions and an incidental exposure condition for teaching targeted vocabulary words to preschool students through storybook readings. In a within-subjects design, 25 preschool students were taught nine vocabulary words from a storybook that was read three times in one week. We compared students' word learning on words taught in three conditions that varied in terms of the intensity of instruction. Our findings indicated that participants showed greater word learning on words in the most intense condition (extended instruction) than words in the less intense conditions. However, there were no significant differences between word learning in the two lower-intensity conditions. Additionally, initial receptive vocabulary was related to scores on measures of target word knowledge.